According to Q&A With Google's Matt Cutts On How To Use The Link Disavow Tool the link disavow tool won't work unless some of the bad links are removed.
What if you don’t try to remove links? Given what a pain it is to get links off the web, why wouldn’t someone just use disavow? I know Google recommends requesting link removals, but from a technical standpoint, if they don’t do that and just disavow, it’s pretty much going to work, right?Answer:
No, I wouldn’t count on this. In particular, Google can look at the snapshot of links we saw when we took manual action. If we don’t see any links actually taken down off the web, then we can see that sites have been disavowing without trying to get the links taken down.