That's a really sad situation. Hope he can get on the road to recovery soon. I absolutely love his youtube content. Personally speaking, I don't think I'd get wound up about some randoms comments on my youtube videos, I don't think I'd care less. This however is not the situation for Mack and it has affected him completely differently. I hope this doesn't get him down and force him to close his channel.
I suppose there is a case to argue that closing his channel could well be the best thing for him, at least in the short term. Going to be hard to overcome negativity from peoples comments or their own videos about his videos, if he is opening himself to them being able to do that. Though that's easier said than done if its his main form of income.