I am so sorry for the loss of your dear husband, and the father of your precious children.
Please try to not dwell on the actual events previous to your husband's parting, his time was then, and you did everything humanly possible to avert the conclusion that came. It sounds like there was absolutely nothing you (or the team that responded) could have done to change his outcome.
Your focus now of course is on your reaction, and assisting your children in dealing with this tragic loss. I can't begin to imagine the pain you are going through. I wish for you great strength and healing in time.
Please try to continue your studies in school. I know this will be challenging! Allow yourself time to grieve, but at the same time if possible, stay in school, and show your children that no matter what, your lives will go on, and their Dad will live forever in all of your memories.