Heroku's consistent user experience post-Salesforce-aquisition gives me a little hope. It would be nice to hear Salesforce offer some assurances of product independence, though.
I can still see a world where Slack is a tool that continues to operate and serve its customers, similar to Heroku post-acquisition, but Salesforce augments their services with Slack tie-ins (and vice-versa).
Short: there's a middle ground I think they can strike.