This is actually a good question and how folks answer it speaks to how they value their life.
Personally, no amount of money would ever get me to agree to live for only another 20 years. I couldn't fathom the prospect of coming to Year 19 and still having a life to live (wife, kids, grandchildren, experiences etc) and then to have all the stripped away from you. In that moment of reflection, it would make the $1b absolutely worthless.
And while it is a lot of money, to what end would it really change your life for the better?
The only thing it guarantees is more financial freedom. It doesn't guarantee you better relationships. It doesn't guarantee you'll make finanically-sound decisions. It doesn't guarantee you won't be taken advantage of where you could ultimately end up not trusting anyone (not even your family). It doesn't guarantee you could lose x-amount to where you're no longer living the life you envisioned.
You could be sat up in your mansion, living a life of instant gratification, but how long will that be fulfilling for? 10 years in and all that shyt could get old, and then you'll be living the next 10 years full of regret, with all that money and not even living.