The turbo would seem to be fairly well protected from such shenanigans. It can't suffer vacuum because the engine would quickly die if the inlet were stuffed. The only other time when it could run relatively unloaded is when the outlet pipe severs, or a waste gate (if your turbo has a waste gate) is stuck open.I've blown several compressor outlet hoses on different pieces of equipment and have never had a turbo failure because of it. What it will do is sound like a cannon going off under the hood when it blows and power will drop a bunch.
Turbos are pretty well designed considering the rough environment, and high speeds they have to run. It would seem likely that it would be hard to over speed one.
I'll hunt down the articles that discussed over speeding turbos and see what I can figure out.
-Chuck