That's not true. You can access the last version of any purchased app from the AppStore -> Updates -> Purchased, regardless if it is available or not on the store for you.
If an app is "completely gone", it probably has a good reason not to be there in the vast majority of cases.
Cold comfort to those who paid for said app.
So want to take away my right for the app I legitimately purchased and downloaded to my PC for later installation ? This cloud BS has really taken its toll.