
Sometimes, and it is worth asking. A tree with an otherwise sound union and a limited crack can often be kept through end-weight reduction pruning plus a steel or synthetic cable installed to ANSI Z133 spec by a qualified arborist, with annual inspection thereafter. It is a removal if the union has already separated, if the cavity is decayed inside, or if the crack runs down into the root flare.
If the crack is over a bedroom, a porch, a patio or anywhere people sit or sleep, treat it as now and stop using that space tonight — split unions fail with no warning sound and often in ordinary wind or simply under the added weight of a soaking rain, not only in storms. A closed, sealed, long-standing frost crack on an otherwise vigorous trunk with a target-free drop zone is a legitimate watch-and-monitor item. The single question that separates the two: do the sides move independently of each other?