I think he will, but there might be a real primary challenge.
I don’t think he’ll endorse anyone except maybe for pay. And I don’t think anyone will want his endorsement. Most of his endorsed primary candidates failed (as I recall, valid to double check that). It may not be a mark of death, but it doesn’t look like it helps.
I can’t be arsed checking/verifying your claim about the endorsement failure, but I do remember something similar, so it’s probably right.