The solemnity of the declaration and the language used by the Pope are enough to convince me of the infallibility of OS. It must be definitive for the future for the Pope explicitly says that the Church has no authority from Christ to ordain women to the priesthood.
If the Church has had no authority up to now to ordain women then it is difficult to see where it is suddenly going to obtain this 'authority' from at any time in the future short of Christ Himself publicly ordering the Church to change its teaching. Any pope who claims to have have had a personal revelation from either Our Lord or the Holy Ghost is going to have an impossible task convincing the rest of the Church.
Leaving all that aside, the experience of the Episcopalians and Anglicans who have ordained women has been catastrophic for those churches. Were the Catholic Church to follow suit it would precipitate the greatest split since the reformation. Look at the strife a mere footnote in Amoris Laetitia is causing.