Good questions...I just went through all of this....it is a little tricky.
With an airbag plug removed, if you start the van, the airbag error light stay on. If you plug in an OBD2 scanner, there will be an SRS DTC for "airbag termination SHORTED" (it is shorted because of the internal built-in shorting bar) .
Then if you reconnect the airbag, you would think that the airbag error light would go off...The thing that threw me for a while is that the airbag light STAYS ON! You then need to erase the SRS DTC code with an OBD2 scanner. I used the INNOVA 5310 CarScan that is available at Oreilly's....about $139..they will match the lower Internet price) If you are in the SF Bay area, you can come over and use my scanner.
The best and cheapest procedure that should not require on OBD scanner is to
1) buy at least four 2.2 ohm 1/2 Watt resistors (Jameco).
2) Then with the engine off, unplug all airbags, cut off plugs and solder in the 2.2 ohm resistors.
3) When you restart the engine, you should have no airbag error light.
A couple of notes. It is very sensitive to resistance...you need 2.2 ohms ONLY. The resistors cost less than $1.Or you can buy the commercially available resistor with matching connectors for about $120 if you can't solder.
I have not replaced with cockpit only curtain air bags. If anyone has done that, I would be interested in how they did that. My understanding is that curtain airbags are optional and not required.
Let me know if you have any questions.