What happen if the Feasibility Condition not satisfied and we can not pick a feasible successor?
A feasible successor is just a backup route. Feasible successor routes are not used to forward traffic, only successor routes are. It is not necessary to have a backup route. If the successor route disappears with no feasible successor, then it triggers a recalculation and reconvergence for that route (queries sent to neighbors), and it may be possible that there is no other route to that destination, causing the route to be dropped.