Very sad. Did the person who died have other conditions?
Doing neti regularly is helpful in any case as preventive to wash out virus/bacter from nasal cavities, then gargling with similar salt water. Straight vinegar sounds very harsh on the mucus membranes! I have a home made mouthwash using pepperming, spearmint, thyme, and wintergreen essential oils. Varies according to my mood. Plus of course water, a bit of 180 proof (1 T to 16 oz water) and a bit of caclium carbonate. Gargling with something like that should do the trick. People can use other Eos like Euc, oregano (gack just a little of course). I use about 20 drops to 16 oz of water and even then dilute the mouthwash in a cup with water.
Many EOs are so potent that even a few parts per million can kill stuff, did research a long time ago about it.
the thing with the neti is it’s a combo of salt and baking soda to produce the correct pH. Recipes are readily available.