They don't have to accept anything. Employment law hasn't gone out the window, it's a change in contact terms they'd have to accept. Players are unlikely to be accepting wage cuts of 75%, at best part of their salary will be deferred. There's also a moral issue, although this is football so probably not being considered. The implication is that clubs will save money by letting player contracts expire and no signing player as they usually would over the summer.
Not playing games doesn't eliminate all costs. Clubs still have to pay in the region o 75% of player salaries (going off average L1 wages), staff for social media, ground maintenance etc will still be working. How many non-playing staff are here at a club like ours that are currently furloughed? Can't imagine we've got a huge number of staff at the best of times.
No games means no TV & radio money, no streaming money, no sponsorship, no advertising. There will be nothing coming in. So the question becomes what are the additional costs of staging matches and how does that compare to the revenue it would bring in.