Exit procedure from Belgium

If you come back and try to live somewhere the police will probably eventually issue you a summons. So, probably when you do come back, you should go to your old borough and work it out with them.

A summons for what? Leaving?

Deregister not w of course. You can do it by email.

"A summons for what?"

@ Mickey, as someone who is so knowlegable about taxes, you should know well. As the person hasn't "de-registered", they are still considered resident in Belgium, and therefore remain liable for Belgian taxes.

Actually it is a summons to "regularize your position" that I was thinking of, a "convocation" in French.

The passport office won't know but if someone else registers at your old address the commune will be confused.
Why not write to them and say you didn't have time to return your ID and how should you do this having left and seek their advice they must have procedures for such thing and better ask them than people who may give you incorrect information

Do not worry. You wont have any problems in the future. If you were renting last place of residence for sure someone else moved and as soon as the person applied for registration the commune removed you after the police visit. I have a personal experience with that. Another option is once your card expired and you did not ask for renewal you will be removed from registry.
So in any case I would not worry about that. Its easy to leave but pretty difficult to setup residency depending country of nationality

If you haven't deregistered, you are still considered resident here and will continue to be liable for income taxes and social security on your income. If you have a bank account with money in it, they will eventually take it if you owe them anything. On the other hand, assuming you were working in Belgium before you left, you may well be due a tax refund due to the fact that you did not work a complete calendar year. You will lose that if you don't deregister and file a tax return. You would be well advised to formally deregister and get a form "modele 8" which is a formal declara

If you haven't deregistered, you are still considered resident here and will continue to be liable for income taxes and social security on your income. If you have a bank account with money in it, they will eventually take it if you owe them anything. On the other hand, assuming you were working in Belgium before you left, you may well be due a tax refund due to the fact that you did not work a complete calendar year. You will lose that if you don't deregister and file a tax return. You would be well advised to formally deregister and get a form "modele 8" which is a formal declara

If you haven't deregistered, you are still considered resident here and will continue to be liable for income taxes and social security on your income. If you have a bank account with money in it, they will eventually take it if you owe them anything. On the other hand, assuming you were working in Belgium before you left, you may well be due a tax refund due to the fact that you did not work a complete calendar year. You will lose that if you don't deregister and file a tax return. You would be well advised to formally deregister and get a form "modele 8" which is a formal declara