The employees might not get paid. The burning building is the administrative building. The idea might be to knock out the power distribution, rather than the reactors. They would want a blackout, not Chernobyl 2.0.
This power outage tracking site isn't showing a blackout across Ukraine (at least as of 10 minutes ago). Disclaimer: I found this site at random - I have no idea of its provenance nor trustworthiness.
IIRC the Russians have stated that they want to avoid any possible UDF provocation at the site - preventing what we might call 'Chernobyl 2.0'.
The Russians took over the actual Chernobyl site a few days back, with the same expressed intention.
But the Zaporizhzhia Nuclear Power Plant is HUGE: the Russians must have an eye on the strategic possibilities of cutting power if they wanted to.