My update hang at 34% last night and I have not attempted another one (no DJ Khaled!) I have a working setup and resetting zwave is not one thing I'd like to do this weekend.
@bcopeland may chime in at some point with official guidance
Non-official answer / Jason's opinion:
If it were me I would do a graceful shut down, remove power cord for 30s, start up, wait a minute, then try the firmware update again.
Yeah, I'll give it some time. I'm not at home to pull the plug anyway.
I sucked it up and tried the update again... and it finished this time!