I was told directly by an agent that balance due dates were being delayed until T-3 weeks, although he said that it had not been officially published anywhere.

Despite that, we have had a balance reminder this week for a holiday on 7 May which is the usual timescale - maybe because the May schedules haven't yet been decided. I'm not sure where we stand on this one - I assume we can get a voucher if we choose to cancel ahead of any cancellations by BA. There is never any info about hotel cancellability in any of the BA confirmation emails or non-flight vouchers although I am pretty sure the hotel is cancellable from a screenshot I took when booking.

Editted to add that I had missed the Twitter responses above - I assume we can apply for a voucher for the amount paid so far. We are clearly not going to be going anywhere in 5 weeks time.