I don't know ... 0 boost? That would be a massive leak. How could the car still run? I would be more inclined to think that the bypass is broken, the blower drive shaft broke or the belt snapped.
That is what I would do ... have an assistant run the car. Stand off to the side of the engine bay (out of harm's way). Have them brake stand the car just enough to get the vacuum to drop near 0. Does the blower bypass valve close? If not, that's probably where the problem lies.
If that is inconclusive, take the blower belt off (if it is still there), and see what happens when you try to turn the blower pulley. If it doesn't spin, the SC is seized. If it does spin, then the blower may be ok.
Next, take the blower top and upper IC tube off (as a unit). Inspect the rotors for any obvious signs of damage. Hold the rotors in place with one hand and try to spin the pulley with the other. The two should not be able to spin independently of each other. If they do, the drive shaft or coupler is broken. (Some of the couplers do allow a few degrees of "bounce" before the rotors will move - don't worry about that. They are spring-loaded. But the pulley should not spin freely more than, say, 10d before the rotors move.)
This work won't be wasted in any case because you have to do this to get to the intake manifold anyway.