Ive had it happen recently, we both just took it as a mercy and went to respawn, its fair, nobody gets shot at close range, your back in the game after a short wait.
Id still probly do it the same way in a non respawn or limited respawn skirmish game.
Think of it this way, with real steel if two people come around the same corner at the same time and one shoots te other, it might not be an imediatly fatal or incapactitating wound, the wounded person can still possibly shoot back, or in getting shot his hand twitches pulling the trigger shooting the other. Both are hit both are wounded or dead.
Skirmishes are generaly short, its not that big of a deal that you haveto sit out for a few minutes, you can take the time to socialise with the other people who are out.