It's normal for the revs to fluctuate as you remove load from the engine (as you take an auto box out of gear or turn off the air conditioning).
A failure of a key part in any car can cause it to stop suddenly and I wouldn't say the Omega is any more or less prone to it than any other car.
A MAF failure wouldn't cause this, as the engine management system has a strategy to deal with failure of this sensor. The main couse of problems, and a sensor which doesn't have any "limp home" strategy is the crank sensor on a V6. Even then, they give warning signs, such as troublesome starting and trouble codes before they fail suddenly in most cases.
If you want to be proactive against this, I would check your crank sensor to see if it has the original cable routing up with the oil cooler pipes. If so, the sensor is likely original and it's worth having a spare as the heat from the oil pipes will eventually cause the cable to break down. If the cable is routed up the side of the engine bay, this has likely been changed before and it should be reliable as long as the cable has been routed away from heat sources and secured properly.
Another thing you can do is check your engine for trouble codes regularly and change the sensor if any related codes appear (these do not appear to light the EML so you need to check for them with a code reader).
Kevin