While you're at it, could you also have a look at a similar issue in Novigrad? It's nothing to do with The Heart of the Woods quest, but the outcome is essentially the same, with one of the hostiles remaining unkillable and getting up again and again after a certain amount of time or distance between him and Geralt.
It's an optional -or at least I think it's one- encounter that's triggered when you have saved two of the Beggar King's henchmen from being interrogated by a group of Witch Hunters somewhere in the Novigrad Docks district. Saving the henchmen from the Witch Hunters isn't a quest or part of a quest per se, but I guess the game keeps track of whether you killed those interrogating Witch Hunters anyway because some time later the game spawns another group of Witch Hunters near Hattoris shop -Red Arrow on the map segment below- who want to take you in.
Geralt may respond with something sarcastic like "To what do I owe the pleasure" or another less sarcastic answer, which results in the Witch Hunters attacking you. The "last man standing" of this group is another case of unkillable and getting up again and again, just like Sven.