Azure web roles and vm durability

Assume we have extended RoleEntryPoint class and overridden Run() method. As the documentation states,

If the Run method returns, the role is automatically recycled by raising the Stopping event and calling the OnStop method so that your shutdown sequences may be executed before the role is taken offline.

I have some questions regarding this

1. What happens to the vm instance if overrode Run() method returns? (Is the vm reclaimed by Azure or shutdown)
2. Is a webrole allocated to a dedicated vm instance or a shared vm instance?
3. Are vms used for web or worker roles are created in an adhoc manner or recycled instances which were created and used earlier? (In this case can we expect old registry key entries are available?)

What happens to the vm instance if overrode Run() method returns? (Is the vm reclaimed by Azure or shutdown)

Your vm instance will reboot in this scenario.

Is a webrole allocated to a dedicated vm instance or a shared vm instance?

You get a dedicated vm instance based on the size your selected.

Are vms used for web or worker roles are created in an adhoc manner or recycled instances which were created and used earlier? (In this case can we expect old registry key entries are available?)

When you create a new deployment, you will get brand new virtual machines i.e. created from scratch. Thus you can't expect old registry key entries to be available.