Hi
Usually route table entries learned and entered by a Dynamic Routing Protocol like RIP has an age time, not like the static - permanent entries.
And Usually this age time out is a configurable parameter.
Now if any route entry flushed from the routing table, router will wait for other router to send him an alternative path, thats why they call RIP protocol, Route by Rumor.
Unlike RIP, OSPF will send a multicast asking for an alternative path for an aged entry in its routing table.
Good Luck !!!