If all that is impermanent is unsatisfactory, then is all that is permanent satisfactory?
All 'things' are impermanent and unsatisfactory (and without self - these are the first three of the Four Dharma Seals). Your subsequent reasoning is wrong* and not Buddhist teaching either - Buddhism teaches neither nihilism nor permanence (one aspect of the Middle Way).

The point of the teaching of impermanence and unsatisfactoriness (and no-self) is to encourage you to give up your attachment to things as a source of happiness and security, and live within the fourth Dharma Seal, 'Nirvana is tranquility'.


Wrong in standard logic ('All Americans are mortal, therefore all non-Americans are immortal' - a fallacy known as 'denying the antecedent': https://en.wikipedia.org/wiki/Denying_the_antecedent ), and wrong with respect to the 'four possibilities', which are brought up in Madhyamaka philosophy simply for the purpose of being denied.