If you are paying month to month and actually check the Terms of Services of those services, most of them can shut down instantly without notice as long as they stop billing you.

A whole lot of Heroku's best features shipped after they were acquired. They had a pretty good run under Salesforce for the first few years.

It would be interesting to hear a full oral history of when and where things went wrong after that. I expect the original founders leaving was a major factor.