Will it be possible for humans to fall from heaven?

No, it's not possible. The reason is because the New Testament teaches so clearly that those who are elect and saved will be kept. It isn't that we couldn't change. It's that God won't let us change. He won't let that rebellion happen. He is faithful, and we will endure. That's the doctrine of the perseverance of the saints.

This doctrine of perseverance is usually thought of as referring to our time on earth—that is, from the time we're converted until we die he won't let us apostatize in any way that will cause us to lose our salvation. If that is true on earth, how much more in heaven! He wouldn't teach the doctrine of perseverance here and then withdraw the doctrine of perseverance there.

So I say with Jesus that nobody can pluck you out of his hand (John 10:28); and with Jude, that God is able to keep you from falling (Jude 24); and with Paul, that God is faithful and he will sustain you (1 Corinthians 1:8-9) and that those whom he justified he glorified.... Nothing can separate us from the love of God in Christ Jesus (Romans 8:30-39).

All these clusters of teaching are guaranteeing to the elect, to the regenerate, that they will never be lost.