My father has Parkinson's, mild to moderate dementia, carotid stenosis, diabetes and a lung condition they've yet to identify. He was hospitalized last year and was nearly septic from a gallbladder infection. The only symptoms seemed to be lethargy and mild confusion for one day. Then a low fever. He is also at very high risk for stroke from a blocked carotid and they've deemed surgery too risky. Now every time he's more tired than usual or seems more confused I consider taking him to the ER. But I don't want to put him through that unnecessarily so I just worry and fuss over him looking for further signs.
I will be truthful with you that this is in fact how my brother, at 85, died. He had been diagnosed with probable early Lewy's Dementia and was doing well, quite with it, and living in ALF, enjoying his two rooms and his activities and a good friend, his ex, who lived in the same facility. Always an avoider of hospitals and doctors all his life (I am afraid even as a nurse I am the same) he avoided letting anyone know about a small non healing wound on his shin. He self treated it for some time according to his friend. He got sepsis, it advanced and killed him within two weeks; antibiotics were of no use against it. So yes, of course, this can happen from ANY infection from sore, to tooth, to UTI and etc.
My brother longed, actually, not to have to go on knowing that his diagnosis meant further serious losses for him in the future. He was "ready" to go and would have given the thumbs up to this relatively quick exit.
There is much to consider in how long we live, how much quality there is to our life, how much taste we have for the continuous losses of old age, ending eventually with the loss of our minds and our very being.
Wishing you good luck with this difficult question.