If Russia goes on to threaten Germany, then it's pretty much Germany's own fault. They've allowed themselves to end up in a position where they are so vulnerable. If Germany cared in the slightest about national security and cybersecurity, it could have easily made defenses far too strong for Russia to threaten conventionally or in cyberspace.
Also, if Russia directly threatens Germany, then Europe will certainly respond as they will not allow a new Eastern Block to form. We weren't in the position to stop the Russians from making an Eastern Block in 1945 (which is why we had to let it happen) but this is not the case in 2017.