I saw some heart wrenching speculation that given his advanced dementia, it was not impossible that in the last week he "discovered" his wifes death multiple times over, leaving the room to do something, then forgetting all about it and coming back and finding her dead for the first time again.
Dementia can be (is) complex, there is a lot of different scenarios for his final days, for example he might have been aware she was deceased and even who she was but had lost the ability to process such a situation, bewildered because he couldn't find the words to explain the situation so did nothing, etc. etc.