IF XT reaches the 75% supermajority, Core will absolutely, positively adopt BIP 101 (or an alternative which is compatible with > 1MB blocks, such as BIP 102)
You can of course continue to run 1-MB-Cap-Core if you choose. Bear in mind, though, that this is not the first hard fork. Users who are running Bitoin Core from 2 years ago are on an alt-chain, just as you will be if you choose to stick with the Core version you have today. (Again, IF XT reaches 75%)
It could still be argued that XT is the alt chain. It even has a new name and branding, which never happened before. This huge schism also didn't happen before. Bitcoin's value comes from consensus, is that consensus based on its fast transaction utility or it's store of value? You can buy things with Bitcoin now, Bitcoin isn't broken.
Even if 75% is reached, it can't be 100% sure that the Bitcoin core chain won't retain its own value and consensus. To say otherwise would necessitate the use of crystal ball 2.0 technology.
That's not to say that the odds of higher value wouldn't rest with XT, because it probably would (assuming the 75%)... but the swathes of people who are hoped to come to Bitcoin are still some years away. There are still many in the Bitcoin world who have educated themselves on the technology enough to know that XT hasn't been tried and tested yet. Why wouldn't they hedge their bets so to speak?
XT needs to pretty much totally eradicate core, but if core still keeps a 'hardcore' group value (sorry for the pun) what's to stop core going to the exchanges as a group and saying 'Hey, we've got nodes, we want representation, and we're called 'Bitcoin', not XT, not Bitcoin fudge, just Bitcoin, and we can prove it.
Many exchanges have alts that are worthless (Correction: virtually worthless) and questionable in their existence, yet the exchanges still list them, will they turn away Bitcoin core that still has value - and considerably more value than the vast majority of alts?
Bitcoins value comes from consensus first, and yes, one of the reasons for that consensus was its use as a transaction ledger for payments, but it wasn't the only one. Ideology played a large part, as does store of value that can't be messed with... yet it is true to say that XT messes with the idea of that store of value.
I can only see that logically it'll pay to hold value in both chains and wait and watch. Yet if a group of us does that (which this poll can be seen to show will at this current time) then core retains value, and if it retains value read above.
The XT discussion is a circle essentially, because the consensus value of Bitcoin itself is circular in nature.