Sure, I get the moral directive that Kirk lays on M5. However, I don't think that much time elapsed between Wesley's report and their retreating outside of phaser range - which is a considerable distance.
The only options for the crew of the Excalibur are
1) escape by shuttles
2) escape by primary hull detachment
3) escape by beam out to friendly ships
1 and 2 didn't occur so that leaves 3. It is possible during that time when M5 turned to chase Potemkin that Lexington and Hood moved in and beamed out the survivors. If that is the case, then this is an interesting example of the ability to beam a whole bunch of people by a starship(s).
However, I'd imagine the dead bodies stayed aboard for Kirk's strategy to work.