Sorry to hear about your dad, but if you want to get rid of the car and get the price then I'd suggest you advertise it on uksaabs and on here but put on plenty of pictures and tell everyone what's working and what's not (aircon, elec windows, heated seats etc.), also what's the service history like? Also do you know if it has the Aero turbo fitted (the '98 run out models did and this could be one) if it does that will make it worth a bit more. Another common problem is rust on 9000's, around the windscreen and the front wings get crusty so what condition they are in might affect values. Finally where are you in the UK?
I'd say a realistic price is anywhere from £600 - £1200 (that's at the high end if it's a bit rough around the edges, but possibly achievable if it has a good history and you get the ABS light sorted, I always found FPT 9000's to have a heavy clutch) depending on MOT and tax status too.
Actually, don't advertise it on here... I might want to buy it