My opinion on how Season 3 would start...
First of all, please forgive me for my poor English.
We all know that a determinant character means that he/she could be saved some point but then will eventually be killed/lost. In S2E5, both Jane and Kenny could be killed depends on how you play.
There are 5 endings:
1. With Kenny---Stay in Wellington
2. With Kenny---Stay with Kenny
3. With Jane---Let family in
4. With Jane---Not letting family in
5. Alone
Therefore, I think that Season 3 could start with Clem and AJ only. Perhaps (and very likely) Jane/Kenny will be killed in Season 3 if they were alive. Since the locations are different, but only Ending 1 is staying in north in coldness. All other endings are without snow (I don't think winter passes in just 2 weeks), so Season 3 could start in somewhere south.
But one thing can sure: Clem and the baby (and Christa, hopefully) would be the only character from the previous seasons that live on. I think Clem is going to be in Season 3 because Clem has always been the centre of TWD. Without her would mean a sale drop and losing money means a lot to a company.
Other opinion:
Season 1 is about protecting and teaching Clem
Season 2 is about Clem protecting herself and teaching herself how to deal with people
(Guess) Season 3 could be about Clem protecting AJ and teaching him how to survive and what she knew
In that case, Clem would be something like 16-18 years old so she could teach and protect and AJ would be grown up enough to learn how to play this TWD game of his life.