As for Blair, I expect McDyess to start next game, just like I expect him to against the Lakers. Other than that, pre All-Star break at least, Blair will probably remain the starter. But long term, I can't see him being in the playoff rotation.
If it's not going to eventually be Duncan-Splitter for a good amount of time against bigger front lines, then this team can't be taken seriously as a contender. It's that simple. The best team in the league is that because they have the biggest and best (when healthy) front line in the game. Playing Blair (at all) and Bonner for long stretches next to Duncan isn't going to cut it.
If he had his hands full with Milicic, wouldn't it stand to reason that Bynum would be even more of a challenge? And he'll have to guard Gasol in stretches. Both are taller and longer and in the case of Bynum, he's also 20-25 pounds heavier.
If it comes to that (Lakers-Spurs), Duncan is going to need every bit of energy he can summon and every bit of help he can get in the paint.