Welcome to FT, flyerpts!

You can do a mileage conversion to get your miles/points from "x" to "y", but you would probably lose many in the process. (Your 10,000 miles in "x" may only convert to 1,500 miles in "y"! )

As MM suggested, keep both accounts active, and continue to earn mileage via partner activity and other offers.

Of my (current) +250K in my UA account, only 52K is from actual flying! The rest are from other activities such as regular credit card purchases (food, gas, clothing, etc...), the UA "shopping mall", car rentals, hotel stays, dining, and (when offered) double and triple mileage promotions! A similar situation is with my +200K in my DL account!

And that current total does not include all the awards that I have redeemed, including sending my sister and her fiance to Asia!

With most programs, as long as there is any activity within 1 1/2 to 3 years, you can extend the account (and miles) for another 1 1/2 to 3 years! ^