Well if only was unmounted from a host instead of doing it from the vCenter Inventory yes, this is the problem.
The problem is that the object is still referencing the Datastore that it doesn't more in the vSphere environment.
A nice solution for this, is to reboot the affected ESXi host but since you deleted it...
I would recommend you to go to the affected host, but maybe you can try and see if still the datastore in another host.
You can check it with: esxcli storage core device detached list and check the UID, it's the same as it appears on vCenter?
If it is, execute: esxcli storage core device detached remove –d naa.UID
By the way, which type of datastore is?