A lead is added to an engagement program stream 1, they progress through stream 2, and finally into stream 3 via the transition rules. The lead has now exhausted all content for all three streams. After stream 3, the lead is removed from the engagement program.
Can the same lead be put back into the same engagement program, progress through all three streams, and receive the same content (emails) over again?
No, this is not possible. By design, Marketo looks for the email ID and only allows the lead to receive the same email once. You would have to clone the old emails so that Marketo thinks it's a new email and add the new ones to the engagement streams. You can then add the leads back on to the engagement stream and they will receive the new emails.