Understand the behavior of SDN in case of network reset/re-configuration

Internet2 required to understand what happens in case:

• ONOS is restarted manually
• ONOS dies and needs to be restarted
• switches disconnect
• A network administrator want to change the network configuration (i.e.) inserting or removing a BGP peer/speaker in the network. In this case, since it's not natively supported by ONOS what he should do? restart a module? restart ONOS?

What does happen in the cases above? Flows are removed from the switches? Anything happen to the routes?

The story is considered completed when we have a full detailed answer to these questions.
Ali for southbound, Brian for intent framework and Pavlin for BGP routes can help with their answers, but anyway an empirical experimentation is needed.