I think season 6 might have followed Leverage International and introduced some new characters to fill in the gaps, but who knows.
The series made it 5 seasons without a single cast change, aside from Jeri Ryan sitting in when Gina Bellman was on pregnancy/maternity leave. It's hard to believe they really would've broken up the cast. And really, we've had several season finales on this show that involved the team breaking up, and they always came back together again the next season. I see no reason to doubt the same would've happened again if the show had come back.