Couldn't tell you what percentage are going on strike.

As with most forms of strike action, some people will still report for duty for various reasons, be it that they didn't vote to strike, or feel unable to strike due to financial or other pressures.

Also consider that Crew members who are part way through a multi-day "tour" duty will complete their rostered tour, and won't join a strike while downroute.

Therefore clever rostering of crew already on a tour can also work to minimise the impact of the strike.