Fork doesn't occur under those conditions.
People's choice will be clear and every service will update software in proper time if a fork does occur..
There is no way to know if a miner really supports Bitcoin XT or just pretends so to give a lesson to the tandem and to show that "one does not simply mess with the blockchain" and future attempts will fail too.
Well, then a fork does not occur, no problem...
If they say they vote for xt, a fork will occur.
Then they don't actually mine big blocks....