Ideally any Rondo trade would involve a player we could slot in at PG, or the Celtics would be picking a guy who would be the heir apparent at point guard.
If Houston is shedding salary, using our non-guaranteed contracts to take on Jeremy Lin couldn't hurt.
Otherwise, there will be some okay stop-gap options available for cheap. Aaron Brooks. Devin Harris. Even Jerryd Bayless.
If Rondo is traded, I don't think the team will be in a position to go out of its way to try and shore up the point guard position right away. The Celtics will be foregoing any urgency to win now and aiming to be good in a few years. No need to rush.