Did I not call it
Depending on your assessor, car may be written off.
It could be that you got water through the breather hole of the gearbox, so its thinned the oil, or it could be that the controller for the gearbox, which sits on the side went poof.
Therefore, you are looking at a new gearbox from BMW, or a ZF repair, push for a new box.that will be 40kish.
With regards to the airbag, it could be that the controller which sits between the two seats have gotten wet, or more correctly, the connectors under the seat got wet.
You may find that once the car has dried that the airbag lights will just reset.
I dont think they will write it off, worst case scenario is that you get a new gearbox out the deal.
If the assessor is going to be a twat, they might fit a new gearbox, but charge you what is called a betterment....
I estimate damage at around 60k which would include stripping carpets, cleaning ect...
Only major module in the way there is the EGS, which went poof already