Maintenance mode is not supposed to last all afternoon, right?

Windows Update
We couldn't complete the updates.
Undoing changes. Don't turn off your computer.
Error code: 0x800f0922
I started updating my theme from teh dashboard. the progress spinner ran for ages, then my internet dropped. since then the site is stuck on the maintenance message. I have access to my host's file manager. is there something I can safely remove, and how do I know whether the update itself completed? I'd appreciate a short checklist of what to verify after it's back up.
