The most mundane method of seeing if the pump is working is just by listening to it... do you hear it whirrring away by listening or touching it?

Indirectly, you could set in your BIOS at startup for your system to shut down after a certain temp. Off the top of my head, I believe intel's design limit for cpu temps are 100 deg C. You could set a temp lower... personally I set my PC to auto shut down if the temp goes above 80 deg. That way if my water pump were to ever fail and I didn't notice, I'd be covered.

You could always google the h50 and any problems people had with it, regarding temp, how to tell if the pump failed, etc...

Hope it helps!