"if it was backdoored by the NSA" - are you going to assume it will stay backdoored by only the NSA? A vulnerability is a vulnerability.
This, of course, doesn't make the backdoor a good idea, and back door or not, if someone does get the discrete log for the Dual_EC_DRBG constants, you are screwed.
If Edward Snowden was willing to give up his salary and liberty for what he thought was the moral thing to do then I think it's reasonable to assume there must be many more people within the NSA who are willing to leak secrets for money or loyalty to nation states, corporations or terrorist groups.
Some of those people will have given the Dual_EC_DRBG constants or applications that will crack cryptosystems using that PRNG to 'bad' actors.