Ooh, I actually know the answer to this! I had cancer a couple years ago, and it got really dicey for a bit. While my story has a good ending and I am now effectively cancer-free, I had to look the potential of death clear in the face and start making some concrete plans.

My answer is unequivocal - I would prepare my family for my untimely demise. My wife and I got together when we were young enough that we entered adulthood together and grew that way. There is no me and her - there is only us. This is not some creepy codependency thing. We just became adults whose emotional and mental shapes are highly complimentary. That happens when you are with someone longer than you were not. We also have kids for whom I am the primary caretaker and stay-at-home dad while she works. Both boys are autistic though you might not notice it, and I am their primary coregulator. My family needs me in ways that are not universally true across families.

Most of my plan can be summarized as follows:

• Prepare my wife for life without me. Ensure she has the basic skills that I have taken over in our lives. Impress upon her the notion that while she has been the love of my life, I sincerely hope I am but one of hers.
• Spend as much time with my kids as possible. Cement myself in their memories. Record messages and fatherly advice in writing and/or video for every major life event I can think of.
• Set up therapy and support services for my family once I die.
• Get my friends and family on board for specific forms of help as time goes on. People who want to help do nothing when they do not know what to do. They are more likely to follow through when told, "I know Jimmy really looks up to you. After I die, please take him out for some bonding time at least once a month. He is going to be lost without me, and Wife cannot be a masculine role model like I was."
• Plan my funeral and write my obituary. Make it clear that any of this can be changed.
• Basically, do anything I can to prepare my family for life without me.

I know this is not terribly exciting, but it found that what I feared far more than death was the fate of my family without me there to care for them.