I think that this is the key in Seymore's mode and place of death. It is loud, messy, and something that Muriel would be unable to ignore, unlike the many things she has ignored. She may or may not have been upset, but it is not the kind of thing that can be overlooked.
While she has ignored so many things, and continues to live in her happy world, Seymore has been crying out for help with his behavior. He needs the unflappable love and acceptance that only children can give, and instead he has a wife who simply doesn't care, and in-laws that may or may not care, but only about how it may affect their daughter.