There must be a way to delete data permanently in order to protect business secrets. This means that there will be no backups anywhere that hold this data. Otherwise it's too much of a risk to use your service, as good as it is otherwise.
Permanent delete has been implemented for files and Inbox messages. Chat message’s content can be deleted.
Guy Fraser commented
There also needs to be a way to fully delete an entire flow group, not just disable them. And certainly things like files, messages, etc.
Five months and a few days since we started using Flowdock, plus three months using it for two nonprofit/NGO's whose boards I sit on, and I am even more definite than my original impression: the moderator/creator of a Flowdock group needs the ability to perma-delete. A myriad of reasons apply, from simple human error (posting an irrelevant document in an otherwise good Flow) to sensitive critical data.