Incorrect assumption there Vincent.
If the airbag imploded, trust me... you will know about it, the entire casing that houses the airbag will be ripped in the middle
Whats more possible however is either that at some point the gent unhooked the airbag for some reason or that the slipring for the airbag is worn.
There is no magic reset combination to reset the SRS airbag module, however any indy with some basic tools could do it, and he can read the error as well.
The error should tell you whats wrong, either its open circuit at some point, or its currently open circuit (slipring) or the SRS module recorded a detonation of the airbag and the dude put another steering wheel on.
Have you got 2 airbags (one drivers steering wheel, the other passager side dash) as the passanger airbag was an option on the E34
My Rides :
10 F10 535 (mine)
12 F30 320i (wifey)