Firmware update for R7900 with Xfinity modem/router

> [...] After confirming that the XB6 still showed that the R7900 was
> connected and the IP address had not changed, [...]

   Is the XB6 reporting its fond memories of the R7900-as-WAP, or are
those data current?  Restart the XB6, and see if its story changes.

> [...] Not sure if that means it never rebooted, Is somehow stuck in
> the reboot, or if the reboot was complete.

   Until you can talk to its management web site, it may not be possible
to tell.

   If the R7900 is really working (to some extent, at least), I'd cycle
the power, and see if its condition changes.  Normally, the management
web site is fairly reliable, but if the settings got scrambled, it might
die (for no very good reason), but leave other functions operating.

   When that fails, I'd try a settings reset (and manual
reconfiguration).  Note that a settings reset should restore it to
normal-router mode, so, at that point, you ought to be able to connect
to nothing except (power and) a single computer, and reach it with a
"routerlogin" name.

   When none of that works, the last ditch is the TFTP recovery scheme.