What about using SNMP to have LTM poll the pool members for CPU, memory, etc usage?
Finally is it possible configure fallback monitor on dynamic ratio load balancing, in this case if the load configuring monitor stops, what would be the ratio,the last set values?
I don't think so, though I'm not sure what happens if LTM can't reach the devices to poll them. You might try testing this. You could also open a case with F5 Support to ask about this and/or ask to have new functionality created to handle the scenario better.
Aaron