Interesting and reasonable question.
First, you can mine at
http://coin-base.net/infiniteAs far as what happens now, well, you are right, we are asymptotically approaching 0, but that is by design. The reward halves each time. So, we knew it was happening.
The coins are out there, and will continue to trade and be used. The supply will just stop growing... and the hope is that the demand increases.
My $.02