I don't recall or know how much longer. Upon searching for it now, I couldn't find any information. There were vague allusions to months longer or doubling the lifespan, but those didn't cite anything. I'm not sure of the normal lifespan across the different octopus species, but I seem to recall it's generally around just a couple years. Apparently, removing the optic gland was done all the way back in 1977 by Jerome Wodinsky. I thought it was much more recent than that.

Edit: This video has always stuck with me. A single octopus female was observed guarding her eggs for over four years.

https://www.youtube.com/watch?v=lFCQltYMLQk

They are such deeply interesting creatures.