excuse me. this discussion so far is based on your not being able to do any flying with 10,000 miles.

That's sort of a wrong assumption.

Currently United and American are offering trips of something like 800 or 1,000 miles for 15,000 miles.

There are a number of ways to bump up 10,000 miles to 15,000 (idine, mileageplusmall) and you can bump up 10,000 to 25,000 by taking a credit card and using it once and that gives a free cross country trip.

So the question becomes how far under 10,000 miles are they.

by the way, you can keep the miles alive by doing any activity. Normally renting a car can do it. It doesn't matter who you fly. Just rent and credit the airline that you haven't used in a while.