Very good idea to have plans like this in place.
I am in my mid 20s and own two horses. I have some chronic health issues. I still work, and my horses live very nice lives. However, considering my health issues, I may wind up in long term remission, and I may not. But (most of the time) I am stable enough to care for my horses - minus occasionally needing help from one close friend and/or my mum.
The close friend and my mum have both had it discussed between the 3 of us what would ever happen should I keel over and die (lol). The mare I've had for ~12 years would stay, 100%. My BOs daughter and her family LOVE her, so she'd stay boarded there for the daughter to play around with and learn on.
My other mare I have had for 5 years would continue with her free lease/training program at the barn I board her at currently, and continue to be shown by them. If she ever needed to be sold it would be within their program (and my close friend/mum would wait until the perfect person came along, though more than likely she would just stay free leased or on training/showing board within their program)
It's all good stuff to have a plan for, and I feel like more people - regardless of their current health or financial situations - should be planning for such events.