I had an interrupted regen once after I parked and turned off the engine, fan under the hood running like crazy with loud noise, after a few minutes, didn't know what happened, I restarted the engine and the loud sound was gone, hopefully it didn't do much damage..
"Interrupting a regen" does NO damage of any kind. When the car is moving, during a regen, the flow of air through the radiator is usually sufficient to cool the engine. If the vehicle stops moving, the heat rises, triggering the high-speed fans.
As soon as the engine is turned off,
any regen in progress is stopped. However, the residual heat might require the fans to continue to run. Therefore, if the fans are still running after the engine is turned off, it is ONLY to dissipate residual heat...the regen has stopped.
An interrupted regen will re-start, once the engine is re-started, and comes up to a temp hot enough to trigger the regen.
In traffic, when I hear a regen in progress (fans running, raised coolant temps, RPMs near 1k) I will put the car in neutral, and keep the engine at 2k rpm, to provide sufficient exhaust flow to assist the regen. This may not be necessary, but I like to think the added exhaust flow keeps things cleaner.
FYI, this scenario (active regen while not moving) has only occurred a dozen or so times in 50k miles. All the other regens must have occurred while at speed (over 2k rpm).
The newer, possibly cleaner, 2012 TDI might require fewer regens, but not because of the DEF. The addition of DEF has nothing to do with the DPF, and the number of regens required.