CV joint or drive shaft?

Is a complete new drive shaft now the only thing to do?

Not always. As you surmised in your question, you can sometimes replace just the CVJ part of the axle and put it onto the end of the old drive shaft. This may come in handy where the outer CVJ is bad and the inner is good, or visa versa. You can sometimes save money by just replacing the single CVJ ... however, in practice, most of the time it just make sense to change the whole thing. You have to figure, if one is bad, the other is worn, so may go out at any time. Secondly, you have to figure what your time is worth. It is a lot easier to change out the whole axle (in most cases) than it is to try and change out a single CVJ. I putzed around with replacing a CVJ on one end and it took me an extra two hours after I had the axle out to get it changed ... what a PITB (mind you, I didn't really know how to deal with it ... I got frustrated at one point and forced it, which made it pop together with a pop and was good to go ... sometimes knowing ahead of time can save you big, lol!) Changing out the entire shaft can save you a lot of time and frustration. If the pocket book can afford it, it's not a bad idea.

If there are cv joint problems you expect some worn metal balls or the housing of it?

If I have problems with the joint, really it doesn't matter to me what is bad, the ball or the joint ... it's bad, so needs replaced. I have, however, assumed you're going to see wear on both sides. I would never try to "fix" a bad CVJ, as what you are describing in your question would only be a "stop gap" measure. It won't fix it permanently.