Yes, he was healed. It was something like 300+ hp restored and heal was applied on the same or next turn. Loic was heavily debuffed. After first heal I recast DT but it didnt help.
That heal was powerfull enough to kill him. I'm not so good in english, what did you meant
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The heal spell effect would still play if Loic healed another NPC

Any other NPC's heal should damage him too? Because I often kill enemies with DC+regeneration.

Can find saves just before fight but I'll try to reproduce bug.

By the way: should 100%+ resist heal enemy while decaying touch?