W.O.W., the point is that he should be considerate enough to let you know and hopefully he will feel badly if he lies. You really don’t know if he is telling you the truth or not, and what can you do about it. The best that you can hope for is to try and instill in him a need to still be considerate. So yes the best you can do, whether you predict that he will or wont, is to continue to ask him to be considerate.
So when he leaves ask him to “please call me later to touch base”. If he says “I don’t know where I will be”, say “it doesn’t matter call me from wherever”, if he says I don’t know when I will be home or if I’ll be home say “call me later before I go to sleep so I won’t worry, its the least you can do”. If the Chevra wants to stay in this yeshiva they probably wont be able to stay out all night and still go there. However, they can stay at each others homes and still go there.