IANAL. You probably know this already, but C&D's are not legal documents - just scare tactics. The result from ignoring it for >48hrs would simply be Facebook escalating... if they decided to.

I have worked for places that have completely ignored C&D's with no repercussions.

That being said, Facebook can use this down the road as an example of them providing ample warning and notice to the developer – which, yes, is something that a judge would consider. There just aren't, say, specific legal outcomes to ignoring this C&D's (totally arbitrary) timeframe.