For it to have happened so sudden, and based on the whirring sound, I would guess that the friction material has come off the friction rings in one or more of the brake packs or clutch packs. If so, it will be easy to find shreds of it in the oil pan. This transmission could potentially be fixed by replacing the friction rings. You have to assume about $500 in parts (frictions, gaskets,seals,piston,fluid) + about 8 hours of labor. This in addition to the R&R.
phoenixhardparts.com , sells a rebuilt transmission for the E430 for $2195+shipping.