There are not 5000+ strikers, as someone suggested....there may be (unverified as unofficial ballot and possibly unfair as not anonymous) 5000 no-voters, but we all know that only actually equates to about 2000 who have the courage of their convictions and will strike.
Let's just say, for arguments' sake that it is 5000.....that leaves 8500 non-strikers.
Having not done a single day's work since joining BA almost 5 years ago when at least one entire cabin crew have worked either just one short haul sector out OR back (often with standover attached, or done a quick Paris and back, go home type day, where the pilots almost ALWAYS work an extra 50%, sometimes an extra 300%.... I would imagine that the current 13,500 cc workforce could easily be stripped back to 9,500 to provide the full schedule- assuming that BA bring in a sensible contract that is benchmarked in the fairest way to be similar to other cabin crew jobs in other airlines- within the very generous confines of the law obviously- in this way BA should expect 900 flying hours from it's crew per year, rather than what is anecdotally around 500 at present for short haul.
With the reserves from the holding pool and temps-to-permanent plus the very east recruitment of laid off UK CC from other carriers, I'd imagine BA coukd run a full schedule within a few months- especially if in the interim it operated to legal limits on crew compliments- simple