“Loyalty” should not be the primary reason for travel. Cost, convenience and amenities are only some of the factors which I believe are more important in terms of choosing a flight which is right for you.
I am really not sure that Delta Air Lines will miss any Diamond Medallion — or any other elite level status members — who migrate to a different airline as a main airline. The reason is chiefly due to the billions of dollars in ancillary fees which comprise a significant portion of its revenue...
...and guess what? It is not the Medallion elite level status members who are paying those fees — regardless of how many thousands of dollars of spend they contribute to the revenue of Delta Air Lines annually in terms of airfare, which I would guess pales in comparison.
Let’s face it: frequent fliers comprise only a small percentage of the customer base of Delta Air Lines; and before the advent of ancillary fees, contributed a larger portion of the revenue.
Of course, I may be incorrect; but that is simply my opinion.
I wish you all of the best with your new choice in airlines, Esltroy.