I'm not sure if I agree with the above reply. Just because Air Berlin is going to join OneWorld does not mean it will partner with Alaska. On the other hand, AA is already partnering with Alaska. So AA miles will be able to be used for Air Berlin flights, as well as other OneWorld flights, while I'm not sure about Alaska miles.

In any case, AA, Alaska, and BA miles don't expire as long as you have mileage earning or burning activity at least once a year, year and half, or whatever. (You can take care of "activity" in Europe in any of these fairly easily by crediting a hotel stay here or a car hire there to that airline once in a while. And, in the case of AA or BA, you could simply credit a short Air Berlin flight to one of them once in a while, and that would keep AA or BA miles alive too.)

Most other OneWorld airlines have miles that you can't keep from expiring no matter what you do, which could be a problem for you if you don't fly OneWorld often in the future and thus don't get to an award level before the miles earned on this trip expire.