如果离开丹麦且没有注册地址居留卡立刻就无效了吗

官方网站上是这么写，

Your residence permit can lapse for three reasons:

If you give up your residence and leave Denmark
If you fail to enter Denmark no later than six months after you were granted a residence permit
If you stay outside Denmark for an extended period of time

Your residence permit will automatically lapse if you no longer have a residence in Denmark - that is, if you sell your home or terminate the rental contract of your home, and you are no longer registered at a Danish address with the Central Office of Civil Registration (CPR office) - and if you leave Denmark.

那我离开后才注册一个地址会不会还有用啊，还是他们系统自动立刻就知道了啊。。。。。还是基本上你不说他们也不知道啊

我觉得你纠结到疯了。不如现在立即买个机票明天回来吧，我敢肯定你可以出境的。