Orrantia, McNeil and Risner could have used the easy fix available to them - fire .357 instead of 38spl +P out of their .357 revolvers. Although for Risner - his primary weapon was his S&W 459 semi-auto.
McNeil took Matix out of the fight with 38spl rounds. Matix didn't fire any shots after he was shot be McNeil. So in that sense - it didn't make a difference what caliber bullet McNeil was shooting through his revolver. What made the difference there is that he had to disengage in order to reload, he wasn't able to put shots on target while he was reloading his revolver and he got hit with return fire.
With Mireles you can make an argument that it didn't matter because he ended it with 38spl rounds, so obviously 38spl was good enough in final moments of the whole thing.
Risner initially was firing 9mm from his 459. It's not clear if Risner or Orriantia hit Platt, causing him to drop his .357 magnum. It makes sense to me that Risner fired this shot, I know that both Risner and Orrantia were fring at him but the next shot - the fith wound that Platt incurred was definately from Risner.
The shot that either Orrantia or Risner made on Platt that fractured his radius bone and exited the forearm, causing Platt to drop his revolver - either Orrantia made the shot and it wouldn't have made a difference if it had been .357 magnum or not since it was a shot to arm that exited out the forearm, or it was Risner - who was shooting 9mm at the time. Either way I don't think a .357 magnum round would have made a difference.
The next gunshot wound to Platt was IMO the only time in the shootout where an argument can be made that .357 would have made a difference over 38spl.
The next hit on Platt was made by Risner who was probably firing his 38spl at this point. The bullet penetrated Platt's right upper arm, exited below the armpit and entered his torso, stopping below his shoulder blade. The wound channel may have been very different with a .357 magnum. It may have shattered his shoulder blade, although who's to say? A .357 mag bullet may have simply exited below the shoulder - I don't know.
My general thought here though is, if you look at each time the BGs got hit with a 38spl and think how it would have been different if it had been a .357 magnum - in all cases but one, I don't beleive it would have made a difference.