No reaction when I plugged in (other than the charging LED lighting up), but after holding down the power button for several seconds, it was able to reboot and install the update. Whew!
Wifi seemed broken at first (no networks detected, manually entering network info still failed to connect), but another reboot fixed that too.
SD card ebooks work too, so it looks like I'm good
Thanks!
Edit: Incidentally, the firmware version is 1.9.11 (6/1/13). So, a year old. Maybe N289 gets different updates from N647.