Withdrawal of Accepted Paper
I would write in to the conference, explaining your situation and that this is - as you far as you are concerned - a case of force majeure. 

First, you could ask for the registration payment back if they still decide not to publish it (not many chances you'll get it, but if you ask in a professional and nonagressive way, who knows). 

Second, you confirm with them (in writing) that your understanding is that this means the paper is now free and can be resubmitted elsewhere (i.e. a confirmation that the copyright transfer is void under the given circumstances). 

They cannot get the money,  remove the paper from the proceedings and also expect you not to submit it somewhere else.