Integrated motor assist problem

This is my sons car. The red battery charging light and engine maintenance lights came on indicating that the 12 volt battery was not charging. I replaced the 12 volt battery and the warning lights went off and it was running fine. He drove it two days later and the engine maintenance light and the ima light came on. I drove it to a local auto parts store and the error codes read P1570 and P1600 indicating that there was a problem with the ima system. The ima system does not show any bars so I believe that it is not functioning. My question is can the car still be driven even if the ima system does not work? I understand that the mpg will suffer, but I cannot see putting a few thousand dollars into this car for a new battery pack. Thank you for your help.