Hi!
I just made a spritesheet export Python Script; it exports the animation you have in your animation timeline to a spritesheet (it's highly customizable, there's a bunch of options).

It's there: https://github.com/Falano/kritaSpritesheetManager

Feedback is welcome: I'm only planning on adding one minor feature before I call it done, but if you have other ideas I absolutely can make other changes.