I see all of these comments in here telling you that Slack doesn't have a leg to stand on, that you should do your best to stick it to them, that you're in the right, that you should ignore them, etc. Meanwhile, I'm thinking, "If I were in this person's shoes, I'd probably distribute it privately to a few people who might want it, and in spite of all the hard work, let the project die in official capacity."

On principle, I want to side with all these other commenters. Fact of the matter is that time is precious. Glad you're doing what you feel is important to you.