Yes, it is. If you delete the keys, nobody has access at all to the data. The ciphertext is irrelevant.
Said another way: you are trying to fit a centralized-shaped peg into a decentralized-shaped hole... wrong tool for the job.
If your use case does involve this situation somehow (?) then the only real solution is to encrypt it, as others in this thread have pointed out. There is simply no other option in an open-membership P2P network... otherwise the RIAA and MPAA would have long ago crushed BitTorrent.
Other networks have implemented mechanisms for the network nodes to delete files as detailed elsewhere in this thread and I think it is entirely reasonable to say there is more that could be done at the network level to help mitigate exposure. Dealing in absolutes is a dangerous proposition.
The concern I have is about malicious actors being able to access the raw objects held on the Filecoin network. They won't be able to do anything with the encrypted objects immediately, but I don't know that you can claim that will always be the case decades from now.