The expiration of miles is way down the list of relevant details. You can keep your account alive for a 10 dollar transaction.

What do you want from miles? They are worth about a penny a piece.

How much of your life do you want to dedicate to a 500 USD accumulation of 'miles' that are difficult to use for all programs?

At the entry tier level below Gold (50000 miles per year)

Fly the airline that meets you transportation needs the best, and then use the miles the same way.