Sir, I began my basic military training on June 25th, 2015. After four months, my mental health deteriorated, and I went absent without leave for over a month. Once I was feeling better, I returned to camp, but was told I had been discharged. Is there any chance I can rejoin and restart my training?

Under Indian law, absenting yourself without leave from basic military training for over a month can lead to discharge. It is unlikely you can rejoin and restart your training, as your discharge was likely due to your absence and not your mental health. You may want to consult with a legal professional regarding the specific circumstances of your situation.