Allergy doesn’t mean instant death. I have a pollen allergy but the symptoms are sneezing and itchy eyes. I have a nut allergy but the only symptom is an itchy mouth and throat. I still live even though I’m often enough in contact with the chemicals that make my body go “no”.

So if MSG allergy was a thing (which it doesn’t seem to be, based on my quick Google search) then it would not cause people to die necessarily.