The only given in all this is that retirements will continue at a decent rate. On one hand that might mean recruitment continues throughout the year, OTOH if this gets really nasty and the flying plan takes a big hit that attrition might simply mean those pilots already in BA get to keep their jobs.
As someone who is old enough to have has seen up close how BA responded to the impact of Gulf War 1, GW 2, 9/11 etc I will offer one bit of advice:
If you really want to leave wherever you are currently , and you really want to join BA then now is really really is not the time to finesse a joining date....... grab the first start date that BA put on the table.