If anything, I think it makes it less likely Garnett retires. I think he'll come back to play with Rondo again, they seem very close.
KG came back for another shot at a title. Rondo's injury robbed him of that shot. He'll want to come back next year and give it (at least) one more go with Rondo and Pierce.
I do think he loves to play and compete, and he still can for sure. Whatever happens with Rondo matters less than what happens with Paul. I think they have a strong mutual respect and seem to really want to ride off together.
They need a bigger horse than either of them are today to get there, though.
My gut (as good a source as anything these days) tells me that when Wyc looks at his options, the best thing, both now and in the future, is to keep those two together. The benefits are both on the court and in the ticket and merchandise booths.
My gut also tells me that KG and Paul have some influence on where they go, or at least would be consulted and make up their mind before the deal is consumated as to how they'd respond (i.e. trade and retire).
But what makes the most sense is to see if there is a Rondo/1st/cash-centered package that could put this team over, and I think we'd have a nice package for Pau Gasol.