True res is mentioned to exist in the comic; when Roy's skeleton gets golemified they discuss needed a 17th level cleric to raise him without it and mention that they don't know if any exist. It seems likely that it's avoided by the fact that the only person involved in any of the story (and quite likely the only person in the world) with access to true res very decidedly does not control his team's finances and who does or doesn't get resurrected. And also currently doesn't have any particularly reason to be trying to do a true res.

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Because he's too ashamed to face the main person he'd want to resurrect.