This seems to be fairly predictable of this case type. Stabilize it. Monitor it. Watch it pulp canal obliterate (PCO). And the root tip kinda sails off into the sunset. Based on those that I’ve seen, a horizontal root fracture like this doesn’t have a terrible prognosis as long as it’s managed correctly. Meaning the doc keeps his handpiece holstered.
Here’s a couple other older cases with the same progression. The increased density caused by PCO can cause some color changes, not to be confused with a necrotic tooth. No intervention is necessary. If desired, internal bleaching without endodontic therapy can be offered, which of course carries it’s own risks, benefits, and alternatives.
Some of these can be observed in the wild 30 years after the fact.