They may give up, they may not.
I know of an instance where Norwegian parking fines were chased up in the UK right to the end, with the final fines something like 8 times the original ticket. And being Norway that wasn't cheap!
With many northern European countries, parking fines are not viewed as a way of raising money, but as a way to put you off breaking parking rules. For that reason many do not apply just a financial cost analysis, it is about sending a message.
Also, was it your own car in Belgium? If your own you could have issues if you go back with it.
FW