Possibly with stroke if it is not used a lot...You can certainly forget a lot if it's not used...Also I suspect that people with less education would lose more if the language is not used...

Thanks, dear Ronnie, even with stroke, people still use language. The question is that they may forget many things but they still can use their own language.

No, it is not possible to forget the mother tongue.

Not possible, as the development of the brain mainly took place in childhood and mother tongue will get inculcated during that time only. So there is no question to lose command over it whether he/she is literate or illiterate.

I agree with Dr. Dhananjay R. Mishra.

Probably one-third of their total age or more, people are continuously practised and lived their mother tongue. The brain can not easily erase those things (language) which feeding and practising such a long time. That's why, they may forget their habits, friends, relatives etc., but cant loses their mother tongue language.

Dears Mahesh, Dhananjay and Shailendra

Thanks for your comments.

I think it's possible because mother tongue comes form your living environment. If your environmental change and contact from your your mother tongue region has to finish.

In my opinion, one cannot forget his/her mother tongue because it is imprinted in one's mind somewhere deep, though speak many languages fluently.

Happy Mother Language Day, everyone!