The value will not be moved over to the other record.
If the subscribed lead qualifies for a campaign, it is likely to receive the email...at least that's what I have seen, although I think Marketo may have fixed that. To be sure, you should test it on two records you own.
Now, there is a master table of unsubscribes so if both leads were deleted and one came back, it would be unsubscribed.