I have a remote office where the default gateway of the LAN is the HSRP's virtual router. Of course, this means i have 2 routers terminating this LAN who shared the HSRP functions.
I know that in case of failure of the active router, the standby router takes the lead. This is ok for me.
Also we have activated the "interface tracking" feature in case of the WAN link failure. With this one, if the monitored interface goes down, the standby router will take the lead also. It's fine too.
Where it's more tricky, it's when the WAN network is composed of multiple technology, like Frame relay access, converted in ATM PVC and so on. Then, if the ATM goes down, the frame relay access, i think, will never be aware of this failure and the "interface tracking" will never be triggered to failover to the standby router.
Conclusion: It's the job of EIGRP to detect this kind of failure and switch the communications path (from all stations in the LAN) to the standby router.
Where i'm not sure, is if the hsrp's active router will redirect the outgoing trafic (LAN to WAN) to the standby router, probably with ICMP redirect. Is someone knows the behaviors in this case?