If he's not in therapy, he should be. It is my opinion that this is an emergency situation. And, yes, he CAN take a semester off if he needs to, but that decision would be premature without professional evaluation, and could be the exactly WRONG thing to do.
What are your parents doing about this? They may be wrapped up in their own grief, so much so that they're not paying sufficient attention.
Furthermore, your ENTIRE FAMILY needs to process, and to heal. You should know that ANGER is a normal stage of grief. (Read about the "Five Stages of Grief" by Elisabeth Kubler Ross & David Kessler).
Talk to your parents. They need to obtain an IMMEDIATE evaluation of your brother; they can begin with the family physician. They should visit or call the doctor first, to explain their concerns and his behavior. Then they should make him an appointment for a physical (and a depressions screening). Or, the physician may make an immediate referral.
If cost is a factor, TELL the doctor, and ask whether your community has low-cost mental health care treatment options.
Perhaps you could take a semester/year off to spend with your brother, and go to counseling WITH him. That's just one option, but it sounds like he may need the support. Remember, when you moved away to go to college, he lost YOU, too. You could probably use each other's support right now.
Trust your instincts. This is not a time to sit back and HOPE everything will be okay. Get PROFESSIONAL help. NOW.