Is our Mutah contract with a duration of 99 years invalid if it surpasses our lifespan? We intend to terminate it before that occurs, is it still considered invalid?
Bismihi ta'ala
Assuming you are 18+, and if you do a mut'ah contract with a duration of 99 years, it would mean you've lived over 120 years, and if both of you are still verbal and cognizant, once the duration of contract finishes, it you become non-mahram to each other again.
You will need to do another mut'ah contract should you wish to stay together, or nullify it, if still within duration.
The way you nullify it is for male to say to the female "I free you for the remaining period".
And Allah knows best