I genuinely do not believe BA will sack strikers (not least because I don't think there will be any more strikes). Everything BA has done has followed a clear warning as to its intentions and sacking strikers would deny BA any claim to the moral high ground.
If Unite was sufficiently concerned to call off the last strike ballot, then I doubt it will call an unprotected strike.
I imagine if BA does threaten to sue Unite and Unite then calls off the strike, then I'm sure it will claim that this was a complete surprise by BA, even though BA first intimated that any future strike would be a contiuation of the first strike 9 months ago!
As for the ballot result, I don't think anyone is expecting anything else than a yes vote, but it will be interesting to see how the Yes vote moves from the last amount of ~5,700 and whether we get below the 4,000 mark.