The two most common signs of a failing crank position sensor are (A)the engine intermittently dying while driving, accompanied with immediate restart, (B) no start condition with engine
It has done one of the symptoms - no start condition. You said 3 times last week the engine would turn over but not start -thats a no start condition.
While sometimes it will set a fault code and turn the check engine light on, it doesnt do it all the time.
One of the difficulties in accurately diagnosing it is that if it is intermittent failure, then it will only test bad when the vehicle is not cranking, or engine cuts out while driving. Any other time, it will test good.
Other possibilites of intermittent no start conditions are : fualty fuel pump, secondary ignition problem- both of which will also only test bad when acting up
It should be, but you need to be aware that being an intermittent problem, you could encounter a no-start condition between now and when your mechanic can see it.
There is a slight possbility of the crank sensor failing completely before next week. There is no way to forecast how much longer it will last. I have seen people drive with an intermittent crank sensor failure for a year or more, and I have seen some fail within a month of first showing signs of failing...