I hope by the time we'll have immortality we'll be able to easily travel to space and live there if we wish. That will solve any "overpopulation" problem, plus you'll never be bored cause you'll be able to explore the whole universe for centuries and observe it while it changes.
I'll enjoy being immortal and use up the time to do as much as I possibly can. So what if I'll have to see mortal things I've grown attached to die, it happens anyway while you're mortal, you just get over it. Maybe that's bad, but I'll feel somewhat good knowing I outlasted all of the ones who died.
And we never know how it will be. It might be living like a robot with no emotions and it might be better than living as humans now. I'm mainly thinking about the possibility of flying on your own in the future or the ability to transform to whatever we wish to.