Skill plays a factor, but I think you're stretching the limits of believability now. I'll go ahead and say it's impossible for your thief (without perfect defenses, mind you, since they're not important for PK) to solo the well-geared/practiced dual-axe wielding warrior, unless you happen to catch him already writhing. Which, of course, is always possible with a thief. With a mage...not sure what you'd do. Zap the hell out of him I guess, but he'd have to be wounded or you're still dead in a round.