assuming -and this is a massive assumption- we are at the start of a recovery, then even if we ignore that it's likely to be a long and protracted recovery, 100 senior pilots gone - on [say] an average of £100k p.a. = £10m p.a. saved.
If you replace 1 for 1, given everyone starts at the bottom, on £48k (assuming no SSP cadet entries, who you can pay even less to...) =£5m.
QED cost reduction of AT LEAST £5m a year. Alright, hardly a make or break amount for an airline such as BA, but still a decent sum....