There is not going to be an easy answer to this. I am assuming there is no persistance involved.
One approach would be to create an irule that monitors the sessions and checks the UP/DOWN state of each active member of the pool. If one member fails the connections would have to reconnect to the next available member. If the member returned, then you could issue a TCP::close which means that all to the once failed member would reparticipate.
Another approach it track the connections during normal operations. You can incorporate the following example : http://devcentral.f5.com/wiki/default.aspx/iRules/LimitConnectionsFromClient.html