I see a lot of people above who are well-prepared, financially, if one goes before the other. That's a critical act of love to ensure that the one left behind has no financial concerns when that happens. I did the same, but it played out differently than I had prepared for and I will be forever grateful for her support in building up our finances as it allowed me to parent our kids full-time as she had.
Aja's challenge still stands, and I think it's relevant for every surviving spouse - once the finances are square, how does daily life go on?
I had the benefit of raising two pre-teen kids after my wife passed, so there wasn't a lot of time for sadness or personal pursuits. Those came after they got older, with the full reconciliation of the sadness of her demise only this year after running out of legitimate reasons and excuses for putting it off. Those were difficult months, and I think I'm through the worst of it now. At this point, I believe I'll be sad for the rest of my life that our kids grew up with a mother who loved them dearly and that the woman I dedicated my life to is no longer here to live out all things we talked about doing together. Until lately, it had been more an intellectual sadness, now it's the kind of thing that can stop whatever else I'm doing until I can turn my thoughts in a different direction.
The hardest for me in the first few years was having to make every decision solo after decades of having an understanding sounding board. The biggest decisions were the hardest, though even something as simple as "do we go to Disney World for 3 days or 4 days" caused short-term paralysis and anxiety. That had been a 10 minute discussion and decision before. There had been general discussion about if she should move with the kids if something happened to me, but there was no discussion about me leaving my job and moving 600 miles away after she was gone, even after her terminal diagnosis. Both turned out to be good decisions but there was a lot of anxiety along the way. Got through those with a few close friends and family members serving as the sounding board the wife once did.
At this point my kids are a few hours away, mostly launched and I'm living alone. Now what? Many of the things I once thought would be fun to do, or to do again at this point in my life have -0- appeal knowing I'll do them by myself. Days are filled as I wish, but there is no one to recap the day with, cook with or for, kick me out of bed if I'm snoring or too restless, nor to have coffee with in the morning.
I recently went through a phase of asking myself "what's the point now, what's next?" nearly every day. Not desperation, nor a cry for help, more the kind of thing one might expect from an INTJ operations guy

. I did what I intended to do as far as raising the kids, now I have to figure out the next big thing I need to accomplish. Starting to think it may be as simple as getting to end with all the fun and joy I can find, but likely without the kind of companionship I treasure. Maybe more than that will develop, and I'm keeping my options open.
The advice section/TL,DR for those reluctant to consider the one being left alone:
-Maintain/build/rebuild family relationships. Siblings, close cousins, nieces, nephews. Parents, if you still have them.
-Keep your close friends close. Call them, go see them. You can pick up right where you left off years ago.
-Get to know your neighbors. Look out for them, the good ones will look out for you.
-Accept the possibility life won't work out as you expected and you'll need to make adjustments, maybe big ones.
-It's OK to be sad, do your best to avoid anger at changing circumstances.
-One can't control everything life serves up, but influence everything you can