I see two possible outcomes. If (almost) everybody agrees before the fork that BU is the way to go, then it will become BTC and the Core chain will die.
If we can't agree and the fork occurs i see no other way then BTC and BTU, even if BTU will be far larger. A switch back to BTC or XBT (which might be more correct) later on seems possible, but only if the core chain will die.
Of course there is also the possibility that there will be no fork or that BU will remain a small altcoin after the split, because after the split it is up to the users which chain they use. If most of them want to stay with core this will have an effect on price.
Core will not give up until they exhaust all their options which include changing the PoW, regardless of how popular BU is before the actual fork.