If Schumacher retires, its a done deal.
If Schumacher doesn't retire, it could still happen, but I find it hard to believe it could since Ferrari is a team that lives around Schumacher. Their second car is just there to act as a blocker for anyone that could challange Schumacher and to help with pit strategies.
Next year on Mercedez, it could be Kimi and Alonso which would probably be a good thing, because mercedez tends to not push team orders and both cars are out there to win.