Alright, I'll take a shot at it. Anyone who makes it to heaven will be there forever.
1 Thessaloninians 4:17
After that, we who are still alive and are left will be caught up together with them in the clouds to meet the Lord in the air. And so we will be with the Lord forever.
So, if a trip to heaven lasts forever, this means one of two things.
1: Humans don't have free will in heaven and thus will never sin.
2: Humans have free will and will choose the right decision forever.
If the second scenario is true, there will still be temptation to a certain degree even without Satan. There was no external "Satan" to tempt Satan; he decided to sin of his own free will.
Now if you sin while you're in heaven (hypothetically speaking), what will happen is quite simple: you get thrown out just like Satan.