Sticking your head in the sand and hoping that the property tax return will pass you by is not a good idea. The tax offices may have a lot to do with the property tax, but that doesn’t mean that they don’t do it thoroughly.
If you do not comply with your obligation, the tax office will remind you and probably threaten a penalty. Attention, a fine can be up to 25,000 euros, you should not risk that.
It can also happen that the tax office estimates the values for taxation and this should turn out to be to your disadvantage. It is also possible that the tax office will charge you a late fee. Either way, if you submit the property tax return in good time, then you are on the safe side.