Driving under low load/low RPM will not hurt anything with the supercharger offline. At MOST, the oil should be changed asap (possible fuel washdown past piston rings.)
So... here's what it looks like when a Dinan tensioner fails:
Note the uneven space between the rotating arm and the clockspring part of the tensioner.
When the clockspring becomes worn with age, the tensioner gets loose in the fore to aft direction. This motion under load, compounded by the fact that the pulley is rounded (why did you use a rounded pully Dinan?!?) allows for the belt to fall off the front part of the tensioner. When that happens, it's a crapshoot to estimate what else will be damaged by the flying belt.
It's time to either:
A. Put the pulley on a lathe, and make it flat (for future use with the new tensioner.)
B. Source the pulley manufacturer, and fit a comparable one that has lips on the edges. (Like other S/C kits for domestic musclecars.)
For now, I have a new Dinan tensioner/pulley assembly on the X5, (Dinan part # D315-0315) and she's back to full power.
Hoping this helps someone else,
- an X5 noob