The 50 seaters will go away when the leases are up and they are no longer economical to fly. But for now many airlines and leasing companies still owe millions on these things and so they'll be around for a while longer.

I do think they'll slowly disappear as nobody is making them anymore (thankfully) and they'll be replaced with larger machines.

But I would expect 50-seaters to be around for another decade, at least. Probably much longer.