Can debris in the mass airflow sensor shut the car down?

Two main items to check on:
1. Don't overfill the oil when it gets changed (3 qts is plenty on a gen II). Verify the level is BETWEEN the two spots on the dipstick. Not too low, not too high
2. Replace your engine air filter

 

What kind of debris?

If the engine air filter is intact, if it is installed correctly and there is no damage to the housing, then there is no way for debris to reach the MAF sensor. (However it can get oily if the engine oil is overfilled for a long time...) It is easy to install the engine air filter upside down, in which position it will not catch everything, so maybe the former owner or some Kwiky Loob doofus is to blame.

Did you buy this car from that dealer? If so it makes me wonder what else they didn't inspect before selling it to you. It would be prudent to return it to them and insist on a complete inspection for free. If they resist take it to a different dealer to inspect it and don't ever go back to the first one. If you bought it privately consider this episode a reminder that *every* used car should be thoroughly inspected before buying, and then take it to a dealer for inspection. So many things can be wrong on a modern car it'll make you ill.

If the correct year Owner's Manual did not come with the car buy one from a dealer. It's full of stuff you need to know. If you don't have the Scheduled Maintenance Guide see here:
http://smg.toyotapartsandservice.com/

 

exactly what do you mean by shutting down?

Loss of engine power? Suddenly everything turning off? Lots of warning lights?

 

The MAF absolutely can take out the engine. I stopped to help
a lady on the side of the road a couple of years ago and as much
as I poked stuff with a voltmeter and eyes/ears/etc I couldn't
get her going; like an idiot I didn't think to pull the air filter
and look down the throat and it turned out later that some small
bits of leaf debris had lodged in her MAF and that's what did it.
The thing is *very* sensitive; even waving a finger over the
general area of the opening can radically change how the engine
runs when idling, so I've gotten paranoid about the thing.
I detail easy inspection/cleaning in my 100K maint page.
.
_H*

 

This manual is free and good:
http://john1701a.com/prius/documents/Prius_User-Guide.pdf