If you strip the threads in the frame, a good engineering firm would helicoil them for you.yes the holes are even in the same place tho with Yamaha motors the thread is in the frame so you strip that then you need a new frame.
any competent bike shop should be able to remove stripped bolts as you could just cut them in half with a dremel cutting tool if they was that bad.
Not necessarily. For example my KTM has two bolts threaded directly into the motor, and three bolts threaded into the frame, with no nuts anywhere. The Cube could be just the same.on a bosch bike the motor is held on by bolts that go through the frame and motor so the only thing that can be cross threaded is the bolts on the other side and they cost 6 euros