Piscotty-Bourjos collision

[jchamp]

Last night, (September 28th) in the game between the Cardinals and the Pirates, which is part of a series that will likely determine the pennant race between the two teams, with a 0-0 tie in the seventh inning, two outfielders collided making a catch near the warning track. There were no runners on base, so the out ended playing action.
I'll probably never end up in a play with such implications, but I will likely see outfielders collide violently, and possibly with runners on base. In the referenced play, the player making the catch immediately signaled for help for his unconscious teammate. My question is, if you had seen such a collision, would you immediately stop play and award bases, allow play to continue until its natural conclusion, or something else? What are the approved actions in different rules sets?