Firstly, if the cryptography is compromised the least of my worries is remaining anonymous; you would have alot of other things to worry about.
Secondly, there is something called "stealth address" oh and of-course if that cryptography is broken well then sir you have more more to worry about than remaining anonymous.
Thirdly, see 1 and 2 and oh yeah why not send a note to Satoshi about it whilst you was as it about how dumb his idea was of creating a crypto currency.
That is a very common fallacy. Or maybe you just have nothing to hide?
When the cryptography securing on chain anonymity is broken, everything in there will be revealed. New algorithms will be implemented to secure everything else from future attacks like your coins so they can't be stolen, but what has been put into the chain will be there and can't be made anymore secure.
You are missing the point again ... when you cannot find any weaknesses is the design of both CN/Shadow you have to resort to breaking the one thing which fundamentally makes crypto currencies secure.
But if you want to play this game lets play.
For arguments sake lets say ECDSA is broken ... so now for every address that has ever made a transaction we can derive the private key.
So as a average crypto user; I could simple import this private key into my wallet and reindex. Voila! I now have every transaction that address every made. Good luck with your dual network or whatever you call it as simple chain analysis will reveal all!
Now try doing that with a solution that uses ring sigs and stealth address. You have to break a single algo to deanonymize DRK and yet would have to break multiple to have the same effect on CN/Shadow.
^ see how your logic is flawed! just like the masternode design.
Darksend does not reuse addresses.