What is going to happen if he claims I was at fault?

You cannot be defaulted while serving in the military. The case would go on until your return. You should notify your insurance however of the accident and the facts.

Get a copy of the police report for your files. Notify your auto insurance of the accident, and if they ask, send them a copy of the police report. Keep the original in a safe place, just in case. If you suffered any injuries, go to a hospital ER or to your family doctor to make a record, just in case. Then go off to boot camp with a clear mind. Thank you for your anticipated service to our country.

If the other fellow ran the red light, then it is unlikely you are at fault, and he would have to prove fault to have a viable case against you. Also, MI requires he have a "serious impairment of a body function" to qualify to make a claim against you (in addition to proving you were at fault). So under your fact scenario, it is unlikely a claim will be made. Nevertheless, if a claim is made, you, or your representative, should simply turn over the claim letter or suit papers to your vehicle insurer, as well as the insurer of the owner of the vehicle you were driving, and the insurer(s) would defend the action. So if you will be out of town, or the country, be sure you have someone taking in, reading and responding to your mail in case any claim/suit comes in (because if you don't answer, the other side can take a default against you). Also note that there are certain different rules that apply to cases if you are not around as you are in the service.

If he sues, turn it over to your insurer. If you receive a ticket in the mail. Hire an attorney to work it out for you.