In many situations, if a non-star player goes down with an injury, you simply plug someone else into the lineup and make do. This isn't one of those situations. You don't replace Marquis with one player because this year's edition of the Celtics is build a lot like a Rubik's Cube. To move one piece, you have to move two others with it. Then you might have to move several more pieces around before you finally get the desired result (and you are still far from being done).
Headed into the offseason, the Celtics had 3 priorities. Get help in the frontcourt, get a backup wing, and bring in someone to help with bringing the ball up court. Sheed took care of the first priority and Daniels was supposed to take care of the next two. Now we've got some pieces to shift around.
Daniels brought the ball up with the 2nd unit and allowed House to play off the ball on offense and guard 1's on defense. Now House has to bring the ball up more (making him less effective) and Doc has to find ways to have either Ray or Paul on the court for most of the game. That will be a challenge when he's also trying to keep their minutes down to keep them fresh for the long run. Of course you could also just run Rondo for 40 minutes a night and pray he doesn't twist an ankle.
In addition, there's a hole at backup wing. The C's have no shortage of guys that can fill in here. First there's Tony Allen, who for all his faults can still provide defensive pressure on 2's (when healthy). Then there's Scalabrine who is better suited for the 4 but can fill in at the 3. Then there's J.R. Giddens who might be able to help us a bit in the rebounding department. Or you could call up Bill Walker from Maine, but he may have fallen behind J.R. on the depth chart (if only because of his preseason injury). You can also experiment with using Hudson at both the guard positions but I'm not sure the team is comfortable with an expanded role for him yet. None of these guys is an ideal solution, but that's why they are backups to begin with.
So what about the option of going out to pick up a player? The team has the assets to make a small to medium sized move with expiring contracts (Tony, Scal, Giddens) but that option has been on the table since the Summer. You have to think that if Ainge were to be forced into making a deal, he wouldn't be in the best bargaining position. He's better off (from a value standpoint) waiting till the trade deadline (by which time Daniels might be back anyway). Of course, if the right deal came along that made sense for both the short and long term, you pull the trigger, but that would be the case even if Daniels was fully healthy.
Lastly, there's the "break glass if needed" option of suiting up Ty Lue to take over the backup ball handling duties. However, to do so you'll have to cut Lester Hudson or someone else off the roster. I get the feeling that the team would like to hold off on this option unless all other potential solutions come up dry.
Further complicating matters (in perhaps a good way) is the impending return of Big Baby. He doesn't directly solve any of the problems created by Daniels' injury but he adds depth to the frontcourt which in theory could have a good trickle down effect on the rest of the team.
Once again, I don't envy Doc or Danny trying to make all these puzzle pieces line up and match when the pieces keep changing on the fly. The good news, however, is that the setbacks this team has faced thus far can be overcome. The short term might prove rocky, but the long term still looks promising (which is a lot easier to say after an 8 game winning streak). Lets see how the rotations look in February, which might again be different than how they look in May and June. Here's hoping the pieces all slide into place just in time.