Before looking into the vacuum pump, I would double check the fidelity of the rest of the vacuum consumers. If it were my car, I would disable the central locks and see how the shutdown behaves, disable cruise control and see how shutdown goes, and then look into the vacuum shutdown actuator on the ignition assembly. Any reason to think the vacuum pump is bad aside from the delay in shutdown?

Edit: I didn't directly answer your question, but yes there are other issues you should look at (and can do yourself with a reasonable ease if you are level headed and willing). The vacuum pump supplies vacuum to several consumers. Any leak in those consumers (main line off the pump, brake booster, egr, climate control, central locks, ignition shut off, transmission modulator, few others I'm forgetting) would all have the ability to change how your shutdown occurs.