If you happen to have high-enough elite status at another hotel program:
But the other question is: Are you really getting that much value out of Diamond over Gold? (It depends in part on someone's travel pattern as to how much of a difference it might make.)

And is June 30 a goal for it for some reason? It matters how many stays or nights you have by Dec 31, not June 30, as to whether you get back to it "eventually".