Playing devil's advocate, I think Balpa will have a hard time arguing against the use of absence, and here's why.
It is not only perfectly legal but a recommended way for a company to differentiate between its staff. The fact that pilots are proscribed from going to work when unfit is irrelevant because the same rule applies to everyone, it's a level playing field. All easyJet is doing is differentiating.
I absolutely agree that there are potential safety implications but I think that will be argued to be a separate issue and doesn't impinge on employment law in the here and now. It remains that professional pilots are obliged to observe the ANO.
Like I said, just playing devil's advocate. I think a poster above made a good point. The 15% of trainers are probably safe and the 5% with conduct issues (a realistic percentage in any industry) are probably not so that leaves the remaining 80% of pilots to make up the other 20% of redundancies.
My guess is that an element of LIFO will be added so it's not solely down to attendance. Fingers crossed there will be ways found to mitigate the headcount reduction.