Data on a blockchain won't ever be deleted. A deletion is just another transaction saying certain data is deleted, so that the world state database can remove that data. Since a blockchain is basically a Merkle Tree, it plays by those rules and is immutable. Data will always be there unless the ledger and transactions are removed from the machines, such as restarting the network and removing all the information from the peers. That's basically a wipe of every machine that was used for the network structure holding the ledger.
However, that's in theory, and it gets a little complicated with different implementations of a blockchain. When you're working with Hyperledger Fabric, if you set an ACL rule or use encryption, then a marked asset might as well be deleted, since there will be many barriers for a random participant to view that data. So depending on how sensitive your data is, it may not really matter.