Transition screen is not shown regardless if the transition is configured to popup a screen.
Conditions and are bypassed but validators are still applied.
The selectde selected transition is executed after the email is sent. Failure to send the email will skip the transition. Although, the failure to execute transition will not prevent the emails from being sent.
It may be a good practice to add transitions to the workflow statuses that hidden from the user interface and executed only when emails are sent.