Here's how I understand it:
* If Pierce plays in 40 or fewer games this year, the deal is completely non-guaranteed;
* If Pierce plays in 41 games or more, the deal is guaranteed for $5 million;
* If the Celtics don't elect to waive Pierce by July 1, 2013, his deal becomes fully guaranteed.
I'm not aware of Pierce having an opt out, and the sites I trust most don't say that he has one, although some sites have reported that he can opt out.
TP! Thanks for the info, so Pierce should be on the books for his $15M next season. Was wondering for flexibility/MLE/BAE. Looking like we'll have the mini-MLE and BAE next offseason, smart of DA to save it.