Im 50, irregular period, endometrium is 11mm. if still do not have period for the next 2 months, will the endometrium lining become thinner by itself?

Usually not: When a woman is having irregular periods close to menopause it is common for the lining to not shed completely. This leaves thick lining which you have. Generally this needs cyclic Progesterone pills for several cycles to get it to all shed. This is done to prevent prolonged bleeding and decrease chance of abnormal cells. - endometrial hyperplasia.