Originally Posted by Mr. Dent
Why would they even do that? It's a silly excuse at best and for this plot to work there needs to be a couple cosmic heroes in it as well as the Avengers. It wouldn't be a fun adaptation of the comic if only 6-7 people are fighting Thanos not to mention seeing the Guardians and Avengers interact would be great theatre and off new dynamics for the movie.
Drax and Gamora are almost a necessity to a fight against Thanos, due to insider information about him; and if they're both there, there's no reason that the whole Guardians team wouldn't be there, too.
I'd say it's a reasonably safe bet that the Guardians will at least cameo in TA2.