Well, Arrow has already brought back Colin Donnell following present-day Tommy’s death via hallucination, flashback, evil Nazi parallel version, and another hallucination.
The show has proved in the past that even bodies that have been dead for quite awhile can return after a dip in a Lazarus Pit, and one major character was resurrected that way in Season 7.
How can Arrow bring him back in a new way, short of resurrection?