Are Pokemon usually handed down from parent to child, or included in a Will? What happens to the Pokemon in dormant accounts at a Pokemon Center? If the answer to these questions is: Usually released to the wild, I propose an alternative: Starting with Farfetch’d and Slowpoke, I want to start up a rehab/repopulation sanctuary for these otherwise vulnerable and traumatized Pokemon, until they’ve been taken off the Endangered Species List. Thoughts?

prof-peach:

Good Question! Well pokemon that are left behind by trainers in PC boxes are one thing, they end up at the professors lab who sent the trainers out on their pokemon journey. PCs are just a way to record and exchange pokemon easily, they are not reduced to dormant states and have active full lives wherever the professor lives. By law you must allow pokemon free roaming space, interaction in a safe environment with other pokemon, adequate care, feeding and medical attention if needed. That is a Professors duty to their students and the pokemon in their care. Any professor not adhering to the laws are stripped of their credentials and roles, removed from the premises and their trainers and responsibilities are all handed to a new employee of the FPP (Federation of the Protection of Pokemon).

Situations where trainers pass, old or young, their pokemon are often given the option to be free, or stay with the family of the trainer. Normally they have no bond to the trainers family, and have the alternative of staying with the professor who is in charge of the Lab/sanctuary where they live. Some pokemon wish to be returned to where they came from, so often pokemon are transferred when this happens, to a location close to their home, and they are returned to their original location of origin.
Handing down pokemon in things like Wills is frowned upon. Pokemon have conscious logical thought a lot of the time, and are living breathing things that are free to choose what they want to do. If they love a trainer, and they are passed to the trainers child, then thats their choice on wether they want to respect the wishes of their original trainer or not. Some are faithful family members, others wish to start a life of their own instead of babysit. Its entirely dependant on each individual case.

I like the sanctuary idea, its often what Professors offer up to any and all pokemon who come to them, or at least the professors I have met in my time. Vulnerable pokemon such as Lapras demand huge roaming space and thus are harder to keep safe, but they are often tagged, and monitored by pokemon that are trained to work with them, to keep them safe from poachers. 
Due to intense breeding programs and protection of natural habitat, Slowpoke numbers are on the rise thankfully, but Farfetch’d is still having trouble.
People are offered government grants to set up recovery programs like you want to, its widely encouraged to help the numbers recover.
I strongly advise starting up your idea, all the help we can offer is good! They need humans to help stop the mindless trapping and consuming of pokemon from region to region.
Good luck on your endeavours, its a very noble cause!