Valve is already fully covered, they will honor refunds to the game and any loss they make will be taken out of future sales. Of course it's possible that future sales won't make up for the loss in this case, but Valve is still very unlikely to make a loss overall.
Valve is well covered here. Like any other platform they only make payouts to publishers / developers after a big delay so they'll have plenty of Sony's money to cover refunds.
I guess lawyers at valve had to work extra to come up with a decision, because they're probably going to court over this.