Why would he 'hand it' to William (odd choice of words anyway, as the order of succession is laid down by law, and is not a gift from the monarch)?
Are you implying that his ill health might require William to act as Regent, or that Charles might actually abdicate?
At present, though Charles has health issues, there is no suggestion that these are on a level to require a Regency.
And he certainly isn't going to abdicate.