Hi Jerry,
Not a shocker news 
We already knew that such a thing has a possibility. Anyhow, even if you delete this somewhere in ECC through an enhancement done there itself, the return BDoc will carry the deletion command to CRM again, so there isn't going to be any prevention there.
Also even if you somehow try to stop the deletion in CRM through any enhancement etc, there would be a lot of permutations to consider. According to your system behavior it is confirmed that on every save in ECC, a replication to CRM will be triggered.
/Hasan