What do you mean by Demo email? An email version that is in draft (and not approved)? We might want to get on the same page regarding terminologies here. Check out Marketo's glossary here.
If you triggered a flow with Send Email flow step, then Marketo would send the email out to the person for whom the flow was triggered. You can view the results in the Campaign's Results tab (snapshot below) or in the Person Activity log.
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