The C's went 17-18 in their last 35 games. Looks like they'll finish under 0.500 next year based on that (injuries or not, those old bones will probably be just as banged up next year), without some significant roster changes plus another year of age.
Worse if Ray Allen decides to move on.
The ride was fun while it lasted. 2008 NBA Championship was the BEST season I've ever witnessed and trading for KG/RA was totally worth it just for that.
But its time to move on. Gut the team for Draft picks Danny! No sentimentality in business. 
Oh... Danny... don't forget to trade expensive aging talent (Paul Pierce, whatever is left of KG, etc.) to teams in the West like Denver and Dallas to overtake the Lakers. 
My guess is the Celtics will win 40-45 games next year; they likely won't have the same illusions about being a contender and they'll play with a bit more intensity. They'll probably be the 5th or 6th seed and get bounced in the first round. The East is very weak.
It's also possible they could suffer even more from injuries and drop into the lottery, which might not be such a bad thing all things considered. Although rookies drafted in 2011 won't get to play any NBA ball until 2012 because of the lockout.
Trade Perk and whatever else to move up in the draft..
How high a pick do you think the C's could trade Perk for? Danny would have to feel confident he'd get a player with a lot of potential in return. There are a lot of big men that could go 5-15 in the draft with a lot of star (and bust) potential - but Danny would have to be okay with getting worse in the short term for potential future gain.
Also, unless Perk performs a lot better in the playoffs, his trade stock has to be down significantly after his performance the last few months. Trading a decent young center (albeit a flawed one pretty much at his peak) with a reasonable contract for an even younger, undeveloped big man (draft pick) could work out great or be a colossal mistake for Ainge.