How to prevent mold in ceiling below upstairs bathroom
As long as there's any water leaking in the bathroom, you shouldn't permanently seal up the ceiling in the kitchen. I would be installing an access panel in the ceiling similar to the one pictured below. It would cover the hole, could be painted to match the ceiling but would also provide access to the area if water did leak and you could spray the area with some mold killer. The frame for the access panel could be regular base board molding or something fancier to keep the wife happy.The panel could be regular drywall so if water did leak on it, you could just replace the piece of drywall. If you don't need access to the pipes in the closet you can just repair that hole or install a similar access panel there too.