If humanity ends up with the ability to travel to other stars, Mars is but a stepping stone. It would be the testing ground for almost everything else. There's no reason to view that as temporary. It's necessary and the whole terraforming process would include figuring out a way to not lose those resources to space.

We don't really know how long terraforming Mars would take, but it's conceivable that it could take as few as a few centuries, especially given the advance of tech.

https://en.wikipedia.org/wiki/Terraforming_of_Mars#Protectin...

(some scientists say it could be done with current tech)