There are very few things which could cause an engine to stop, and which would not be a huge cause for concern even if I got it restarted.
Off hand I can't think of any realistic ones, other than idiot passengers doing something like pulling the mixture lever all the way back.
If the electric fuel pump makes it come back then you have a shredded engine driven fuel pump, with debris floating around, so better land ASAP, if possible somewhere with engineering facilities.
If pulling the alternate air (fuel injected so no carb icing) makes it come back then you have a blocked air filter... not too bad but I would head back somewhere with engineering facilities because short of very heavy rain / snow this should not happen, and has never happened to me in the heaviest rain.
Either way, it's a pan call, at least.