If your OS sees it as offline, it isn't a driver problem. You can use literally any driver and it should make it to the printer, and in most cases, at least "something" will print, but at the very least it will get there and fail.
So you are actually troubleshooting a Connection failure. My Guess, is that you are printing via Hostname (probably IPP) and the firmware slightly changed the host name, so it appears offline.
I'm thinking you simply uninstall the printer, and install it again using whatever driver you want, but manually create the port.
Best bet is socket://address:9100 Which is typically listed as a CUPS-raw queue <change address to the IP of the printer>
So in CUPS, Add a printer and choose this thingy right here
And just do this, but use your IP
When completed, if it still won't print, disable this thingy right here if you can find it or similar (I don't have a 6605, but it isn't needed to troubleshoot your issue)
i have linux Mint 18.3 based on Ubuntu.
till yesterday my Xerox Workcentre 6605DN was working properly with a driver i found in linux mint database
I had use driver for Workcentre 7345 without any problem....
i had install last firmware from original of 2012 to the last of 2016
Now under windows the printer work normally as usual but under linux not work
linux (i had try several drivers) see the printer "offline" and noone job sent is printed.
i had try xeroxprntmng in text terminal, i had try there several drivers... noone work
so i have 2 solutions:
1) find the old firmware
2) find a working driver....
can someone help me?
a disperate man