I think both are replaceable if it happens. I have faith in our recruitment policy, that we will come out stronger.
Selling either of those two sends the wrong message to the rest of the squad, prove to them we are serious about being a success by keeping our top players.
IF Tiote & Ba are replaceable then we need to sign those players anyway to strengthen the squad.
In an ideal world yes but I think it will be tough for us. If we "only" make it to EL some other teams will be coming and sniffing around, maybe with an CL offer to tempt with... Well, maybe I'm just pessimistic. I really hate silly season.