Uh, how is this different? These zombies most likely will also offer no support or security patches. Hence the term "zombie". The only difference here would be that you could possibly still download the last version from their site which is not the case with FoundationDB.

As long as you have the latest version and you put it in your SCM or wherever you want to keep these things, you are just as able to take 3 years to migrate away from FoundationDB as you would be from one of these zombies.

At least with FoundationDB, as others have said, you actually know now what will happen in the future, with the zombie you might spend additional time "sticking it out" before you realize they will stay dead. That would be time you could have used to start the migration.