Will all Muslims eventually go Paradise even if they go Hell?
Yes, if they are Muslims in the true sense of the word. This is the belief of ahl-uh-sunnah wal-jamaa'ah. If some people are to be in the Hellfire (which is referred to as 'jahanum' in your question) for all eternity, then they really are not Muslims even if they seems to be so from the outside. The Muslims can be divided in to a number of categories based on how their situation will be on the Day of Judgment:Those will enter the Paradise ('jannah') without being brought to account (the 70,000 (or more, according to some reports))Those who will enter after being brought to account (those who have more good deeds than bad deeds which Allah forgives). The Prophet (peace and blessings of Allah be upon him) said: “Allah will bring the believer close and will shelter him with His screen, then He will say, ‘Do you remember such and such a sin? Do you remember such and such a sin?’ and he will say, ‘Yes, O Lord,’ until He makes him confess his sins and he thinks that he is doomed. Then [Allah] will say, ‘I concealed it for you in the world and I forgive you for it today.’ Then he will be given the book of his good deeds. But as for the kaafir and the hypocrite, the witnesses will say, ‘These are the ones who lied against their Lord!’ No doubt! the curse of Allah is upon the wrongdoers.’” (al-Bukhaari (2441) and Muslim (2768)). Those who will enter after being forgiven by the Lord of the Worlds (because He can forgive whomever He wishes). Those will enter the Paradise after they are punished for their sins in the Hellfire (those who have more bad deeds than good deeds). Perhaps this is the group that you are talking about. Yes, they will enter the Paradise. The people of al-A’raaf (a wall with elevated places) whom Allah says will stand between Paradise and Hell as long as He wills, then they will be granted permission to enter Paradise, after the people of Paradise enters it and the people of Hell enters it. When they are on the wall, they can see the Paradise and its people, and the Hellfire and its people. What Faizaan Datoo said in a comment to the question is not accurate according to the Islamic belief. As for what Harun Urhan mentioned about those who will be brought out of the Hellfire having a mark on them, I do not know of this. Perhaps he would be kind enough to quote evidence for everyone's benefit. :)And Allah knows best.
Why is Satan immune from eternal hellfire?
Hell is now. It is the place where unsaved people (souls) go when the body dies. Before the judgment of the lost (Revelation), Satan, the Antichrist, and the False Prophet (with all demons) will be cast into the Lake of Fire for all eternity. After that, those souls in Hell will come out to face Jesus Christ at their judgment. From there, all those lost will be cast into the Lake of Fire also. Once in, there is no escape, no reprieve, no appeal. Just eternal fiery punishment.
Muslims, why should we believe in Allah, the invisible sky daddy without evidence?
Since when does faith rely on evidence? Lets skip the scientific miracles and tell you a little story... A Muslim man decided to stop his prayers because he claimed that there is no evidence of Allah's existence. With the way this ignorant proud man was beginning to think, he raised up three interesting questions to an Islamic scholar to prove his point. If Allah is real, what is His shape and how come i cant see him as evidence? How could there be such thing as Qadar (written fate) when i can obviously do what i want and control of my own life? If Allah made satan from fire, how does it make sense that on Judgement Day he will put satan in hellfire, as that would not hurt him? Did Allah did not realize this! Without saying a word, the scholar slapped him. The man looked at him shocked with anger and asked why he had slapped him. The scholar simply asked him this: Do you believe in pain? The man said yes. Does pain have a shape or a figure? No. But does pain exist? Yes. Did you know yesterday that i was going to slap you today? The man said no. Did you wake up this morning, or walked in here knowing i would slap you? No. I didnt even know i was going to slap you! Only Allah knows what is going to happen, this is Qadar. The scholar said, let me ask you something, what is your face made of? The man said, flesh! The scholar replies, what do you think my hand is made of? Flesh... When i slapped you, did you not feel pain even though we are both made of flesh? If God wills, he can make satan in pain! It took a single slap to serve as a wake up call for this man, needing further "evidence" is just called a lazy brain.
What is the difference between ' HELL' and ' THE LAKE OF FIRE '?
Hell Definition: The word “hell” is found in many Bible translations. In the same verses other translations read “the grave,” “the world of the dead,” and so forth. Other Bibles simply transliterate the original-language words that are sometimes rendered “hell”; that is, they express them with the letters of our alphabet but leave the words untranslated. What are those words? The Hebrew she’ohl′ and its Greek equivalent hai′des, which refer, not to an individual burial place, but to the common grave of dead mankind; also the Greek ge′en‧na, which is used as a symbol of eternal destruction. However, both in Christendom and in many non-Christian religions it is taught that hell is a place inhabited by demons and where the wicked, after death, are punished (and some believe that this is with torment). Second Death. “The lake of fire” into which death, Hades, the symbolic “wild beast” and “the false prophet,” Satan, his demons, and the persistent practicers of wickedness on earth are cast is shown to mean “the second death.” (Re 20:10, 14, 15; 21:8; Mt 25:41) Initially death resulted from and was passed on to mankind as a result of Adam’s transgression; hence “the second death” must be distinct from this inherited death. It is evident from the cited texts that there is no release possible from “the second death.” The situation of those in “the second death” corresponds to the outcome warned of in such texts as Hebrews 6:4-8; 10:26, 27; and Matthew 12:32. On the other hand, those represented as gaining “the crown of life” and having part in “the first resurrection” are free from any possibility of harm by the second death. (Re 2:10, 11) These, who are to reign with Christ, receive immortality (deathlessness) and incorruption and hence are beyond the “authority” of the second death.—1Co 15:50-54; Re 20:6; compare Joh 8:51.
Did Allah Promise Victory to the Believers?
Yes, and plenty of promises. Allah does promise what's coming..the Judgement Day and does promise much success for those are not only believers but who did strive for Him and succeeded. As well as the rewards, Allaah promises they shall have. The Ultimate winners. The ultimate losers and the winners will have an interesting conversation and people of paradise will wonder about those losers. Allaah will allow them to see where they've ended up from paradise and they will respond to them and will say how does it feels to be among the losers? who failed to please Allaah and failed to strive in worship. They will ask them what made them end up in certain parts of hell, people of hellfire will respond how they didn't pray..how they never prayed or never used to pray to Allaah sincerely. They've neglected their own Creator and worship. Praying is the most important that Allaah will look at on Judgement Day, will make a review upon it..will look at the quality of your prayer and then judge you..plenty of judgment..plenty of questions first.
Is the threat of Hellfire supposed to keep people in line?
It is human nature to think you can get away with something, whether you are an adult or a child. Tell a child that they will be punished if they get into the cookie jar and they will still try to sneak a cookie. Tell an adult that they will get a ticket and have to pay a fine if they are caught speeding, and most of them will still speed. Hellfire is just as effective a deterrent as what I already mentioned. I believe that Jehovah realizes that and therefore, since He is as wise as He is, would find other and more effective ways of dealing with sin. There are a number of ways of looking at hellfire, and to me none of them make sense save one, and that is that it just does not exist.