Wordbird,
No, the airbag it's self cannot be removed. But the great thing about ABS Vario setups (This Dakine is), the pack can zip off and a different can be put on.
Now, of you can buy a Dakine Altitude 40L separately, which has the zip off pack. Then you would have a "Spring'/Summer base unit which the "pack" itself can be zipped on and off.
For instance, I have a ABS Vario now.. I just got the Osprey KODE 22+10 with zip, ABS compatible, pack. It is my summer pack night now on a summer base, then I'll zip off and put on my ABS base in Winter.
Look at the sale price and think "I need a ABS base unit, and I'll get the size of pack later if I want to change".
So I can use it for Spring/Summer and then zip it onto my ABS base unit for Winter.
Hence, one of the big selling points of the ABS.
What's great is there are sales on the other compatible packs later in the year, so you can get the ABS 25L now.. then change to a different one later. You're not stuck with one size.
Hope that makes sense.. I'm a week bit tired.. so my words are not as eloquent as usual.. LoL