Server 2008 DNS

Hi all, I've recently promoted a Windows Server 2008 DC to primary and assumed all the AD and DNS rolls to it. It's working well and DNS is working on it. I have also forwarded the service providers dns to it.
The setup is that it's the only server handing out internal dns to 4 separate locations with 3 locations on Comcast and one on Windstream T1.
If the location that the server is at goes offline I loose internet access at the other three locations (and always did even with the original server). Work station's are setup with dynamic ip/dns.
We use Linksys RV042 VPN's and my thought is to setup the second dns on them to be Comcasts and in the one location WindStreams. However when I add the entry on the VPN routers I break internal name resolution of the PC's on the network and users have to use IP addresses of our Terminal servers.
What I'd like to do is have the other locations still have internet access even if the internal DNS server is down. Is there a way to do this? The RV042's have dual wan so maybe I could use the Failover with different dns numbers and have it go to the same modem or any other ideas?

Thanks as always in advance for any ideas,
Jay