I move your thread to the AS7 space because it is the better location, domain controller has nothing to do with clustering.
I will give you a quick answer to your questions.
If you start AS7 in domain mode there are different processes. Each instance, you might have the domain-controller and many host-controller, starts a process-controller, host-controller and 0-n servers.
If a controller crashes it will be automaticaly restarted.
so in case of 2./3./4. the process is restarted, only in case of 3. you might have impacts to your application.