One thing is to say that the process of the Perl interpreter got an amount of memory from the OS, and other thing is to say that Perl internally uses this memory with a SV, where a SV in Perl can be a data type (SCALAR, ARRAY, HASH, CODE, etc...).

So, when a reference to a SV goes out, yes, this will be undefined/destroied, and the memory (inside the process) used to represent this SV will be used in the future for new SVs.

Now about keep some back reference of who hold a SV, like in an ARRAY or HASH, I say that not! The SV doesn't know if it exists inside another ARRAY or HASH value, it's just a SV.