Unfortunately, there really is no way to know in advance. And even if someone could say "a lot" or "not much"...that's relative. I don't have much loose skin compared to some, but it's enough to make me feel really insecure about it, so.
You're young and healthy though, so your skin does have that advantage. Do you have any loose skin now? That could be a good indicator of things to come, how your skin has held up through this first 50 pound loss.
Either way, it's worth it and most of us have learned to deal with it.