I use a one arm solution ( Trunk interface) in active/standby environment made by 2 CSS 11501, working in router mode. They, each, connect to a separte swicth through the trunk interface. In such configuation, I ask,if configuring critical physical interface is suficient? the switchs are connect through a trunk interface also, and the server and client side are distributed among them in their respectives VLANS.
The trunk with the switch could be up but the servers or the default gateway not reachable.
You could add a critical service for the gateway.