Wise man says: Do not make excuse for open, late or dry cow. Cull at first convenient time.
My practice: open cow, whatever the reason (dead calf, aborted calf, not pregnant) means cull.
Late calvers, whatever the reason, either are sold alive as pairs, or culled after weaning the calf.
If the cow has a difficult calving and gets help, and calf survives, this cow is not as uneconomical to keep around for terminal purposes. She will likely succeed next year, but cows without calves are to expensive to keep.