Implosion seems like a pretty nasty spell to be caught off-guard with, so I'm gonna laugh if Durkon dies again, to a cleric he was politely chatting with no less.
I'd give Durkon a 2/3 chance of surviving it, actually. Given what I've seen of Redcloak, I'd say his Wisdom score would be the absolute minimum for casting 9th-level spells, assuming that Implosion isn't his 9th-level domain spell(it is for the Destruction domain, assuming Redcloak has that domain) and also assuming that domain spell are exempted from ability score requirements(the SRD isn't clear on that one, so I don't know).
Assuming the minimum Wisdom to cast Implosion, then it would have a minimum save of 23(10 + 9th-level + +4 WIS bonus). A Fortitude save negates the effect and Implosion can only target a creature once per cast. Durkon is a Dwarf Cleric. His Cleric levels would give him either a +9 or +10(depends on how far his two recent resurrections have lowered his level). And as a Dwarf, he has a +2 to Constitution(and it's probably fairly high as well), and a racial +2 to saves vs spells. At an absolute minimum, he'd save on a roll of 11, but that's assuming a base CON of 10(12 because Dwarf), and ignoring the possibility of any magical items or effects he might have affecting him. At this point in the adventure, it might be good to assume both a higher Constitution and that he did buff himself up in case Redcloak tried to gank him, hence why I'm giving him better odds.
People on the GitP forums have noted that Durkon should still be under the effects of Wind Walk and that if he were in cloud form he'd be immune to Implosion... except that he's in solid form and it takes 5 rounds to change form and Implosion is an instantaneous effect.