Not sure if I understand this, but let me give it a shot. When you say that the routes still stay in the routing table of these routers when the line from router A to the WAN goes down, this should not be happening. Did you configure static routes only on router A, or also on other routers in which case this would be your problem. Probably showing config of router A would help with this issue. The routes should disappear once the next-hop IP is not reachable, or if the statics point to the se0/0 interface, when that interface goes down, the routes should be removed from the routing tables.
The more important question here, however, is how do the remotes know how to reach your networks ? What is this "WAN" ? Is it the IP cloud within some "ISP" ? Or is it something of a frame-relay type ? If this is an IP connection to the ISP, then I assume the ISP is routing to your main offices and the remotes. In this case you'd need to coordinate with them the routing changes if they know about your networks statically. Or you might want to get their help in setting up a dynamic route exchange.
On the other hand, if we talk about something like Frame-Relay, as long as you have a PVC to router A and router D, all you'd have to warry is you OSPF metric considerations.
Please feel in the gaps so we can help better.
