Is the money that the father receives after the amputation of his leg and his retirement at home permissible or impermissible, knowing that he is able to perform work and will receive his full entitlements?

Your father is not permitted to receive a salary from the company unless it is in exchange for work. He must return what he has taken to the company's treasury if it is a public company. However, if the company is owned by an individual or individuals and they agree to give him a salary without work, there is no harm in that, as it is considered a permissible donation.