Hi,
If I understood well, you want to "reset" all existing connections as soon as all pool members of your pool goes down ?
If that's what you are looking for, then your irule wont work because the irule will run only when receive a "new connection" on the VS.
If you want to reset all existing client-side connections, as "iaine" said you could try to set the pool feature "Action On Service Down" to "reject".
Otherwise, If you want to manage this from you irule you need to call an external script within your irule using iCall for example. Then from this script, you can use tmsh command to reset all connections of a particular VS.
`tmsh delete sys connection cs-server-addr "VIP_addr"`
Hope it helps