...weathering the storm.
Three fights to review in breaking down this upcoming fight are GSP vs Serra 1, Karo vs Serra, and GSP vs Hughes 3.
A fresh Matt Serra is extremely dangerous on the feet, as seen in both GSP vs Serra 1 and Karo vs Serra. Unlike Karo, though, St Pierre wasn't able to survive Matt's initial surge because he tried to continue trading instead of neutralizing Matt's offense. Some might call it stalling, but there's a purpose for holding on until you have your legs back. St. Pierre has likely learned this lesson.
The most effective way of neutralizing a dangerous striker is to take him down. GSP is an agile and powerful wrestler, and coupled with the threat of effective strikes I imagine he'll be able to take Serra down eventually if not immediately. One can't simply look at Serra vs GSP 1 and conclude that St. Pierre isn't dangerous on the feet... overall he's probably the best striker in the division.
Although Hughes might not be the submission threat that Matt Serra is, St. Pierre demonstrated a very dominant top game throughout their third fight. Unless St. Pierre loses his concentration entirely I don't see him getting subbed automatically from guard. Again Serra is skilled off his back but not unstoppable.
I see St. Pierre passing to half guard (either through GNP or straight off the takedown) and mauling Serra with elbows as Karo did. Because of his improved BJJ and incredible agility I don't see St Pierre getting swept. I see him winning this via GNP if he can weather the storm