I would bet my entire BTC holdings that this will never happen. I can also bet my entire BTC holdings that the Core team will not support Segwit2x or any other fork whatsoever. Maybe, and just maybe... the only way I see Core devs departing is if somehow Segwit2x camp manages to force a PoW change in the legacy chain to survive, then technically they would be working in an altcoin, but it would be the best altcoin out there, and basically still the real Bitcoin. I hope we don't have to get there too... it would be a mess.