I tested this in a lab and you can do it all with HSRP.
Firstly if a single subinterface fails I couldn't find a way with HSRP to move everything across to the other router but you don't need to.
All you need to do is if a single subinterface fails you must move the WAN interface across.
If you do then everything will work although obviously both routers will be active and standby for different interfaces. I am happy to explain how it works although it's easier to see it in action to be honest.
However that said it is unlikely you will get a single subinterface failure ie. the main interface or the switch port it is connected to will fail.
So you can either set it up for just the main interface failing or you can do it on a per subinterface failure, it's really up to you.
What you need to do is -
LAN interface is one with subinterfaces
WAN interface is gi0/1
1) create a tracked object tracking the line protocol of the WAN interface.
If you want to track just the main LAN interface created another tracked object, again tracking line protocol, for the LAN interface.
If you want to track per subinterface then you need to create a unique tracked object per subinterface.
You need to make sure that if the track is activated it takes enough off the HSRP priority on the active router so that the standby router now has a higher priority.
2) on each of the LAN subinterfaces you need to add the tracked object for the WAN interface to the HSRP configuration.
On the WAN interface you either add just the LAN tracked object or you add multiple tracked objects, one per subinterface depending on which you want to track.
3) you need to modify the HSRP configuration on all interfaces so that on both the active and standby router you add "standby <group> preempt" .
The above should work.
I tested in the lab using tracking per subinterface and as long as you move the WAN interface across whenever there is a failure of anything it worked.
Like i say if you do get a failure then i suspect it will be the entire interface in which case everything would switch to the standby router.
In the unlikely event of a single or multiple subinterfaces failing but some still staying up you won't move everything across but it will still work.
If you really do want to guarantee everything moves in every scenario then i think you would need EEM but i don't think it is worth it as it just complicates things.
Happy to explain how it would work and if you need a hand with the configuration just let me know.
Jon
