Thanks for the suggestions. I did try all those without any luck. It's a USB printer and just wasn't being seen.
What finally fixed it was plugging the printer's USB cable directly into the mac rather than through USB hub. As soon as I did that it was detected / installed / online. Has been working fine on hub for 1.5 yrs, and other devices connected thru hub all fine still. Tried other ports on hub too but that didn't help.
Maybe it was a coincidence that it went "offline" at the same time as the security patch was installed... Murphy's law?