My mom and dad are still alive but they are only in their mid 50s--they aren't married to each other and I haven't seen my dad in 25 years though. DH's mom and dad are still alive and are early-mid 70s.
My DH's grandmother is 91. Her husband died of heart problems (also a smoker) in 1984, I think...so 32 years she has lived alone. (She never lived alone before, got married at 15...married until his death) She never wanted to remarry, she still tears up every so often when she thinks of her husband.
12 years. My mom passed away at age 69 in July of 2004 and my dad at 86 in July of 2016. My inlaws are still both alive and if my MIL were to die today, i think my FIL would follow within months. He is one of those that cannot take care of himself and relies on her for everything. If it goes the other way and he goes first, I think she will feel some freedom for the first time in her life and take advantage of that. They are both 81 and I hope they live into their 90's.
My own Grandma was like that - she was on her own from 1978 until her own death in 1996. My DDad and his siblings were very devoted to her though and made sure she stayed active and didn't want for anything.