I’m 17 years younger than my SO, so I’ve always expected he will die first, possibly by decades. He comes from a fairly healthy and long-lived family, thankfully, and takes very good care of himself compared to most people I know.
I love him so dearly, but I’m a lone wolf by nature, so I think I would handle that ultimate loss and the grieving process better than some.
When I was a kid, I saw an episode of “Family Ties” where the Keatons are talking about this, for some reason. As I recall, the conversation went something like this:
Mr. K: But I don’t want either of us to die first!
Mrs. K: Honey, logically, one of us has to die first… I mean, how else could it happen?
Mr. K: Well, I always imagined that we’d get real old, and then one day, we’d be sitting on the porch, and we’d look at each other, and hold hands, and say, “One, two, three… die!” - and we’d die.
That’s exactly what I want.
My husband needs to go first, for financial reasons. Not because I have loads of insurance on him, but because he needs what I bring in. If I was gone, he’d have to go back to work (he’s 65 and not in good health) or move in with one of his kids. Or find a woman with some income. 
I’ve already told my husband that if I die first he and the widow next door would make good companions. He’s entirely too polite to comment on that.
Both of us have lost enough close friends and relatives that I think we’d manage the grief part of it all okay. Grief is uncomfortable but not disastrous. Certainly nothing to fear in old age when it is so inevitable.
I suspect that, as it stands presently, he would be better capable of managing financial and household affairs better than I would if I were alone.
All that is subject to change, of course. And there are many options for resolving end-of-life issues these days.
I feel pretty comfortable with whatever occurs since there isn’t a lot of control over the decision.