I don't think it will be a shock exit. I think the bottom two will either be Heather and John, in which case John will go, or Heather and A N Other, in which case Heather will go.
It's clear Heather doesn't have enough public support (shame, cos I quite like her) and we don't know exactly how much John has. The judges won't keep Heather over any of the other contestants - the only possibly vulnerable one is Christine, but even then I think the judges would keep her.
Having said that, my predictions always suck!