I expect that we would suppress it as the site no longer exists...
I'm not really sure what you're saying, but: guitars.stackexchange.com currently redirects here. The message is for users who don't know what's going on when they arrive at this site. It won't stay there for long.
Edit: You mean this message?
I suppose it might make sense to remove the link after a time, but given that the owner may be a "dead" user it's useful for explanatory purposes.
It is definitely useful to keep information that it came from Guitars.SE, but the link should be removed (not fixed, as it would point to the same question you're currently looking at). Also it would be good to have a note that the original site does not longer exist, and all guitar related questions should be asked here at music.SE.