Ozawa's time on the national scene may really be short. More information is emerging that he was personally aware of, and approved some of the dodgy deals under investigation. Prime minister Hatoyama has declared that Ozawa can clear his name once and for all by laying it all out and explaining the whole thing to the public's satisfaction. The implication is of course that would Ozawa not be able to fully explain everything (and the investigation leaks certainly suggest he can't) then his days as a DPJ official may be cut very short indeed.
The only question in my mind is why Hatoyama hasn't taken steps to remove Ozawa already. The DPJ won their mandate on cleaning up and reforming the political process, and this kind of thing is exactly what the DPJ leadership should work to uproot, not take part in themselves. This is the single most damaging thing that could happen to the DPJ and they must be acutely aware of that fact.
For the DPJ it doesn't really matter if Ozawa's dealings have broken the law or not; just their dodgy appearance and the guilty-looking efforts to hide them is damning in the public eye. With the loss of all public trust he is no longer able to function effectively as an elected official. He should realize that and resign. Failing that the DPJ leadership should and resign him in his stead.
Edit: Our Man In Abiko puts it admirably succinctly.