It's owned by Salesforce;n if they stop growing it, it'll go the way of Heroku - and that breach didn't go well.
I actually think Slack is great and it has improved over the last 12 months.
The data it has is incredibly valuable if they build their own product or sell it off. You essentially have org charts of entire companies and people asking for things and getting responses and working back and forth together long term.
In terms of building agents for doing real work this could be more valuable than things like Reddit.
proprietary software that no one who cares about privacy or security should use? absolutely. dead? not exactly