If they want it to go at speed then they can get more output for less weight than with a gas motor.
Only at very high revs, with low torque. If you want to haul around a big heavy vehicle (which this is, and *then* some) you want a diesel.
My Mercedes can suffer complete electrical system failure and still retain all the important features but forced kickdown, and it's got a four speed automatic transmission. Even the vehicles with automatically leveling rear suspension retain this feature, since it's hydraulically driven.
I've done this with one of my old Citroen CXes - I picked it up from the guy I got it from with a blown alternator and no battery. All I needed to do was remove the brass slug in the injector pump for the stop solenoid, and push-start the car, and all was just fine thanks. Well, mostly. After the first 15 seconds or so...
You see, as you point out, the self-levelling suspension is hydraulically driven by a pump on the engine. On old Citroens like that, it's a pump about the size of a coffee mug - about the same size as the hydraulic pump on a smallish tipper truck or farm tractor. This pump also provides the hydraulic power for the steering and braking system. Now, once the engine is running, there's a reservoir that keeps the brakes up for an hour or so, but for the first few seconds after starting one that hasn't been run for a week or so, there's no pressure at all. No brakes, steering locked straight ahead (no pressure means no way to release the steering ram) and no ground clearance...