Should the mechanic have let me drive off with a check engine light FLASHING

I had my alternator and battery replaced together a month and a half ago. The shop told me I had to buy the battery there to guarantee the alternator. Last week I was going over a mountain pass at 1200 feet. On the way down my ABS and brake light came on and my speedometer quit working. I dropped into 3rd gear (manual transmission) so I would not have to break as much going down the pass. My car started feeling like it was going to quit. I pulled over to the side of the rode and was able to put the car in reverse. I turned off the car and when I tried to restart the starter was clicking. But, my car would not start. So, fortunately a nice family picked me and my friend up and drove us into town (we were in a no cell area). I had my car towed to the shop in town (Aspen). The tow truck driver did jump my car and my car started but quit. The shop in aspen push started my car and it started and ran normal. They hooked it up to diagnostics and could not see anything wrong. They told me that the alternator that was installed my be intermittently charging the battery. They had never heard of the brand of alternator put in my car. They have been in business for over 30 years.

I took my car back to the station that had installed the alternator/battery and explained what had happened and what the other shop had said. They said they would look at it. Which I made an appointment 3 days later as I had to work 12 hour shifts. I took it yesterday to the shop. They had looked at my car for 4hrs. Hooked it up to diagnostics and tried to mimic what I said happened on the pass. They said that it read a bunch of different codes. And that there might be a short somewhere and that subaru probably had a more in depth diagnostic code reader. But, that the alternator was working. They offered me a free oil change for my time. When I got in my car. The car wouldn't start right away and the check engine light was flashing. I went to the mechanic and said my car would not start and that the check engine light was flashing when it had not been before. They did not tell me that I could not drive my car with the check engine light flashing. I call the dealer auto service center when I got home. Approximately one mile from the service station. They told me that I should drive the vehicle with the check engine light flashing. Needless to say I was very disappointed and frustrated that the mechanic from the other shop did not tell me to not drive my car. I called the manager of that shop to ask what exactly they did to my car so I could tell the mechanic that I'm now going to have to have my car towed to. I also said that my check engine light was not flashing when I brought the car in. The manager said it was the speed sensor that caused the light to flash and that the car was ok to drive. Basically, acting like it was my problem. I will have my car towed tomorrow morning since it is the weekend.

Also, I am a woman. I'm a nurse and work on broken sick infants. But, don't know about cars. I did not know that I shouldn't drive my car when light was flashing. But, figured the mechanic would know that and instruct me not to. Since they couldn't tell me what was wrong with my car.