As of right now, killing the Siren while she possesses a charmed 1UP! will result in her dying, consuming the extra life along with the familiar, but not resurrecting herself.
Interestingly, that the revive state exist, but there is nothing in the code that would change to it
UPD:Turn's out, the state change is stored not in Update function, but in the UpdateDeath one
As of right now, killing the Siren while she possesses a charmed 1UP! will result in her dying, consuming the extra life along with the familiar, but not resurrecting herself.