The proper question is not what God "has to" do, but what God has revealed.

In a recent "debate"/discussion between Adrian Warnock and Rob Bell [available HERE], Bell (arguing that repentance and salvation are possible after death) asked Warnock the following:

So [you're saying] God has to create a situation-- to be true to God's judgment-- in which there is, for this person, it [i.e. "Hell"] is fixed, it goes on, into the future with no end, and there is no hope,

But this is the wrong question. The question is not what God has to do in some theoretical sense. The question is what God has revealed concerning the truth of the afterlife. We do not get to first decide what things it makes sense to us that God must or must not do, and then read Scripture in light of what we think God has to be like; instead, we must learn the truth concerning who God is and what He has done from His Word, and then let that truth shape our thoughts and conscience.