My own view is that I doubt he will sack many - just a few hotheads on the day who justify it.
More likely is the schedule will be wound down to nothing on the first strike day announced, starting up to 3 days ahead for some parts of the network.
However, ALL cabin crew will be instructed to report on the day, anyone not turning up, INCLUDING those calling in sick, will be deemed to be on strike, and will have their pay, (all pay, not just basic) stopped until they turn up for work.
The company will then assess what schedule they can fly on the basis that many crew will be willing to work, plus others willing to help, and then gradually build up the schedule as strikers realise they can't afford weeks without pay, and they return to work.
A few diehards will be left, slapping each other on the back, trying to get the odd car to toot as they drive past them. (On £30/day)