Isn't all of this just equivalent to a pointer? "This variable doesn't exist" is a reasonable error message when you're, for example, dereferencing a pointer with a wrong data type: it could be the equivalent of "there's no integer at this address" or "this integer doesn't exist".

The problematic "this" is just an indexical in that case, and it works fine in terms of ontology, just like we might say "this house doesn't exist", while pointing at a burned up lot. Any fluent speaker of English will understand that, just like how they'd understand a description of the Parthenon as "this is a great temple", while looking at a ruin.

"This email doesn't exist" is not really problematic; the metadata persists but the body and subject have been deleted, plus whatever else constitutes "a message" in this schema. We can refer to it, because the pointers still exist, but the value at the address is gone.

The house might not exist anymore, but the address still does.