The question is really did the lead get pulled from the Engagement when it was marked as Invalid=TRUE?
Unless you have a campaign doing that, the answer is the email is still active in the Engagement, so resetting the email and setting Invalid=FALSE (which should be an automatic process), will have the lead ready for the next Cast.
Now if you want to restart that lead, I recommend:
- If lead bounces/invalid/etc, pull out of Engagement
- if Email Address Changes AND Invalid=TRUE, then set Invalid=FALSE
- If lead was Member of Campaign 1, and Invalid becomes FALSE, then Add to Engagement Program