You may get error messages because the Most Bus and all the devices attached to it will be broken. The devices are bluetooth , BMW assist, PDC
. The other problem is when or if you have to take the car in to BMW there computer will not be able to update the software or write to modules that have to be replaced in the course of repairs. It looks for the original configuration of the car when its hooked up its not happy if it doesn't find it.
So you need to at least keep the head unit if you
want to be able to repair the car . It is recommended you keep your OEM head unit installed if you don't want to have these problems.
Also if you happen to have the Logic 7 setup there is no aftermarket head
unit that will interface with it you have to get a new 9 channel amp and they
don't make those.
If people really want to do this with logic 7 they will typically install and ms-8
It can be done but you have to do a lot to make it right.