Buy Class C with Delamination if price is right?

Pass unless you are a big risk taker.

It's very likely that the owner and you don't understand the extent of the delam and what could be involved in repairs.

"Will the delamination grow if the leaks have been fixed?"

The correct answer is yes, no and maybe. If the area is dry there will be no further dry rot. But the seams etc are compromised no amount of calking etc will last. If the area was small which this one is not then maybe...