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
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?