@Angelik ******
When you get an extension under education, work, or volunteer, you sign a paper that says you will notify them when your situation changes and cancel your extension. If you just leave without doing that, then you failed to live up to what you said you would do, and if you ever try to get another long term visa or extension, you will be fined 20,000 baht and may be prevented from getting that visa/extension because you lied to immigration in the past.