I would be very suprised if SKY move to a UK spotbeam for exactly this reason - the loss of revenue. The operators interested in moving, and with nothing to lose, are the ones on Freesat - the BBC, ITV et al. that are NOT part of a SKY package. The SKY digiboxes provide these channels but SKY do not opérate them.
Back at the end of last year BTSport moved from Eutelsat to Astra 2F UK spotbeam, A few days later it reappeared on the PE beam - you may wonder why. I'm sure there is nothing oficial published anywhere but as it is a pay cannel I expect that the switchboards were clogged with 'UK' residents wanting to cancel their subscription as they were no longer able to receive the cannel - money talks!
None of the Freesat channels are subscription so they will have no pressure from subscribers or be running the risk of losing revenue by losing viewers outside the UK.
My guess (and it's only that) is that SKY will not run the risk of losing paying subscribers irrespective of where they are based so if they move to 2E or 2F they will move to PE beams. If that is the case then you should not worry about losing your tv.