Since being widowed, I've done some research on social isolation (yup, I'm isolated). Turns out the consensus is, if you're OK with your level of isolation (not depressed, unhappy, lonely, etc) then it doesn't affect your mental health adversely. If you are feeling lonesome, then get some help, volunteer, etc.

I looked on line for a quiz to quantify social isolation, and decided this would be a good one:

You have died alone in your home. Your body is discovered
a) within the hour
b) within a day
c) within a week
d) after the cat has eaten your face, and the smell is horrific
e) by archaeologists in the future