I only speak for myself but if I engage in a 1v1 with a xeno, I fight to the Death.
However, I find this is a rare occurrence. In almost every single fight I have with a Xeno, either additional xenos will arrive to reinforce the original, or the xeno retreats when it sustains any significant amount of damage. Furthermore, around half xenos can match or exceed the top speed of a uninjured Predator (not wearing heavy armour) which further complicates chasing a retreating xeno.
No xeno is going to stand in a fight where they are losing and keep fighting until they die, they will always retreat when the odds start stacking against them. This is fair however.
But it gets annoying when every xeno fight ends the same. You fight a bit, they run away, repeat.
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Furthermore, and again this is personal. But I never see Predators, myself included, healing themselves during a fair, worthy, fight. I only see this when the fight becomes unworthy when the target gets heals or is reinforced.