Is it still more expensive if they just shelve it

Yes. Like, it's not even a question it's more expensive to delay it. First of all, they are choosing to pay for 6-12 months of extra development, which alone is probably several times more money than the bonus that they would have paid out. I don't know what their payroll is, but we don't need to know because math.

If the bonus was for 1/2 annual salary per person (which would be insanely high), then the cost of the bonus would be the same as 6 months of additional payroll. Meaning that with any longer delay than 6 months or smaller bonus structure than 1/2 of annual salary, it becomes more expensive to delay the game. Both of which are incredibly likely in my opinion.

And that's just salary. It's possible the studio was planning on laying people off after release, but more likely that they would have moved to a other project that is currently wrapping up pre-production. So this is causing a cascading effect unless they hire additional staff to catch up.

Then you have marketing costs. The rule of thumb in the industry is that half the overall budget is marketing. There are all sorts of contracts they probably had- digital stuff like banner ads on websites, on the console digital storefronts, partnerships with twitch streamers and YouTubers and review websites, physical stuff like cardboard cutouts and fliers. They may have started printing for boxes for physical releases (though I'm not sure whether this game would have had one or not). They may have started acquiring merch inventory: shirts and stickers and backpacks and flashlights and more perhaps. Some of these contracts they may be able to postpone or cancel, but they certainly aren't getting back 100% of what they paid.

And in all of this time they aren't getting the huge revenue spike they were expecting. The vast, vast majority of a game's revenue comes at launch (excluding live services, which this hopefully will not have). They need to survive another year on the trickle of revenue coming in from the sales of their other games, or Krafton may need to pump more of their own money into Unknown Worlds. Or debt.