You never know.
Sure he might retire, but as so many guys have proven in the past, just because you're retired doesn't mean you have to stay retired.
Say we win it all, July 1st rolls around and we end up with a lockout. KG doesn't want to deal with the lockout mess so he says he's retiring.
After an extended vacation, and some nice R&R, his body feels better, the competitive juices start flowing, and he forgets why he retired in the first place.
Not too far out of the realm of possibility.
Magic Johnson came out of retirement.
Michael Jordan retired after the last lockout, only to come out of retirement for the 2nd time.
Kevin Johnson retired after the last lockout too and ended up coming back.
Alonzo Mourning retired in 2003 and was back in 2004.
Tim Hardaway and PJ Brown both retired for about 3/4 of a season.
I'm still hoping Sheed comes out of retirement

So even if KG retires, there will always be the hope he makes a comeback (as long as it's with the C's).