And they're fragile as hell. Only one simple hit to the ear with a rock breaks it off and a good kick "kills" them. Were it not for their ability to reform, I'd be amazed they weren't an endangered species. Which they most likely are anyways, since the Everfree Forest is their own known home presently in the series.
I know that's how the Timber Wolf King "died" in the episode, but we simply didn't see them reform together again because attention was obviously paid to the mane characters. At most, its an unconfirmed death. I suspect using their wood while they're temporarily "dead" however is a pretty good way to ensure complete elimination.