What Can I Do if There Is No One to Replace Me as Agent Under a POA??

That is a tough situation and there is no obvious solution. We'd recommend investigating what senior service organizations are available that might be able to provide a volunteer guardian or conservator. In a few parts of the country there are public guardians who provide this service. And, if your friend has money, some attorneys are willing to take on this role and they will charge for their time. To find an attorney near you, go here: https://www.elderlawanswers.com/elder-law-attorneys.