Sorry but they signed up for it. Reddit never claims that by moderation you gain ownership. He didn't host the community, he moderated it.
The only reason someone should be allowed to kill a community is of they are the ones hosting it (in which case they should be allowed to decide what they want to host) or if the community is harmful.
It would be like someone who decided to go everyday to the park and clean the benches, would one day decide that he is done cleaning them, so he just tajes them home. They are not his benches, they are not on his property. His contributions are great but they do not entitle him any ownership.
Every provider has it's rules, these are reddits.
And I highly disagree about deleting a community returns it to how things were. The nods are just a important but small part of a community, especially one with a 200000 user base. These users also put energy and effort, they made content and formed connections. Erasing that because one person decided to is unfair, unjust and unproductive.