The school needs to follow due process in resolving an accusation of plagiarism, including a hearing, etc. The procedure should be outlined in your grad school's regulations. Typically, this process can be continued because of ill health or family matters. In my experience, you also can withdraw at any time, which also may moot any hearing; i.e., they cannot proceed with a hearing if you are not a student or are absent because of ill health. With respect to tuition, unless you contracted otherwise, the school cannot accept unearned tuition for courses that you could not attend because of withdrawal or ill health. There would unlikely be any basis for criminal charges. Contact me through my website "higheredjustice.com."