You will not have to worry about running out of LEO. There is, technically, 1B that could be issued although we will never get to that amount. The reward pool is spitting LEO out on a consistent basis and that will continue with a decreasing inflation rate.

One thing that can easily be done is to extend the decimal points out. If LEO, which is at 3 point now. adds a few more, then, effectively, you can use parts of LEO as currency. This will likely be a result of a massive price increase compared to, say, the USD.

Right now there are roughly 5 million LEO out there yet, effectively, you have 15 million transactional units available.