"pop" is a very relative term. My opinion, and it admittedly is not the most informed, is that as long as the car is running "ok", making target boost, and not throwing CEL codes that it's good to go. I don't know what all the possibilties are when a turbo stops working, but I can't imagine that any major damage would occur as long as you realize something had gone wrong and stop running the engine.
Completely different animal, but I had a big-rig turbo go on me, once. Getting on the highway, all of a sudden there was no boost, lots of black smoke out the exhaust (too much fuel getting dumped into the cyliders, nothing major) and no power even though I didn't have a trailer. I pulled off the next exit, no major damage. The braided oil line had kinked and the turbo was toast. New turbo, good to go. Up to that point I had no indication that the turbo was going bad.
Some of the other people here could probably tell you better what the car will do after a complete turbo failure.
I wouldn't change it too early because I would want to get it rebuilt and upgraded (or a comeplete rebuild to bring it back to "new" condition), not just swap for a new used one. But you obviously need to drive the car while the original turbo is getting fixed. That and the fact that you probably aren't going to break down in your yard. If you think you will probably upgrade to a different turbo in the future, I might just swap to a new one without waiting for the current one to break (safest but won't nessesarily last the longest). On the other hand, the current one may be fine for a good long while and it might be a waste of money to go to a new one too soon.
