So, if I got this right I would only have to refill the tires around the time between now and the second coming.
The fact that the nitrogen is decaying is a different problem from it leaking out of the tire.
As to second comings...
Should the wait for redemption have been Prophesied to be that far in the future I am sure St John would have told the story of the cooling embers of a white dwarf star gently warming the atomized remains of the earth for 10^21 years after all earth has been incinerated by the final fusion of hydrogen, then helium, then carbon in the suns core. Each fusion transition boosting the core temperature causing the suns atmosphere to expand; eventually incinerating the inner planets. These mixed solar and planetary remains then expand in a shells of gas and dust to be mixed with the Galaxy like cream in a swirling cup of coffee.
Then Christ comes...