At what point during the iPod touch jailbreak for Windows can you no longer stop and restore your iPod?

Provided that you follow the instructions word for word, you should be able to do a hard restore on your iTouch at any point during the jailbreak.

You are doing somewhat advanced procedures though (check Erica's liveblog on here, and she's a dev!) so don't think that you can't brick your iTouch.