After further discussion we'll be doing a rules reversal on this. There were some additional unintended consequences that came along with this.
To be included within the rulebook will be the following:
If a dude in a posse moves away from the location of a shootout, or moves home, that dude automatically leaves their posse.
What this means, in the situation you bring up above Eli can move to the location of another wanted dude, ending the shootout and avoiding casualties.