I'll argue against this a little bit. It will certainly be less rigid in an impact but I don't think that overall the doors play much of a role in the rigidity of the uni-body beyond that.
The hinges are certainly not attached in a manner that would increase static rigidness... but used as a crush zone it would be very beneficial just by looking at the way the doors would interlock with the chassis.
That said, best thing you can do to a cherokee is put in an internal cage. Takes the slop right out no matter the situation.
edit- this also gives me a good reason to be nostalgic & post an oldschool photo.