If you time out and you haven't been asked the minimum number of questions, you will automatically fail. If you're somewhere between the minimum and maximum number of questions, you may not automatically fail... it will depend upon how you did on the scored questions. So you may or may not have failed the exam.
I believe the minimum is between 70-120 questions for it to be within 95% accuracy of your competency level. You can go out earlier or later, but between 70-120 is the minimum range where it can get accurate results on everyone.
"The NREMT Paramedic (NRP) Paramedic cognitive exam is a computer adaptive test (CAT). The number of items a candidate can expect on the Paramedic (NRP) exam will range from 80 to 150. The maximum amount of time given to complete the exam is 2 hours and 30 minutes. "