I could be wrong here... but... im gonna go ahead and say it anyway!
I am assuming since we can only issue 1 challenge per day (or whatever the restriction actually is) that this means that the gods intended to limit our ability to be in frequent mutal challenges
So to my mind, although the 2 combtants can agree to continue, they would still have to watch out for other attackers, as the challenge is not mutaul (by game rules)
Of course i could be wrong (I normally am!)
Ranger Sugna, Totally Insane
Written by my hand on the 9th of Midwinter, in the year 1072.