Give user permissions to delete a document where it is not linked to another document

Good morning,

I have a specific situation with permissions and want to see if my proposal to rectify this is possible:

We have a certain class of document (not subject to a workflow) that has automatic permissions assigned. The permissions actually prohibit the creator from deleting their own document. The reason is because this document is supposed to be a document that 'supports' different kinds of requests (other document classes). To ensure maximum integrity in the system, we decided that users cannot delete these supporting documents given their importance to 'support' other documents. 

However, we have instances where users, in confusion or otherwise, upload the same document multiple times.

We want to give them power to delete these duplicates or documents that are not linked by a relationship to any existing request.

Are there means to specify a condition that IF a 'supporting document' is not linked to any other existing document, that then the creator should be able to delete it?

Thank you.