I don't think the law system will change a lot. Firstly, I guess most of the "continental countries" have a similar system. The biggest difference is with some Anglo-Saxon countries which use Common Law. Secondly, a lot of the law already comes from Bruxelles. I heard it's circa 60%. They were also a projet of european BGB/CC. So, I don't think it's the biggest problem. For sure, it won't be easy, but it's possible.
Yes it would change. There are some things in the french or italian law for example (don't know how they're called in english) that doesn't really exist in german law. And we have the Abstraktionsprinzip for example, other law systems don't, although they don't have the common law. And so on. There are really a lot of differences.
By the way, there's nothing "wrong" with Alternativ für Deutschland. Even if I don't share their ideas, I respect people who support it. It's not like I was referring to the NPD ... Don't take offense for that : I'm sorry if you did.
I also don't share their ideas.
Tbh I really look up to Merkel because I'm sure a lot of people told her "oh that's not for girls" when she was young.
But she believed in herself and studied physics and became the chancellor.
But of course I just don't agree with everything she does, for example this idea with the United States of Europe.