Dangerous soffit is missing wall insulation

I discover the backside of the soffit wall is missing insulation, allowing a significant amount of heat to escape in the winter. This soffit is above the dining room and originally created a square ceiling for a closet. However, the flipper removed the closet, making the soffit pointless. Unfortunately, it is more work to remove the entire soffit than it is to fix the insulation problem.

The narrow, 15′ long soffit is only toenailed into the rafters, and not strong enough to hold the weight of a person. I’ll have to devise a safe way to access this tight space and fix the insulation problem.