Marc Guggenheim is smart not to kill off Leo Snart as actor Wentworth Miller has already indicated he could come back to the Arrow-verse in the future.
Of course, any commitment he makes largely will depend on the availability he’ll have now that his other show Prison Break is confirmed to return for Season 6.
At the time the actor made that statement, Miller said he would need to be convinced that it was necessary for Snart to return considering so many avenues of his character had already been explored.
At the same time, he also stated he loved working in Vancouver, where most of the Arrow-verse shows film, so he may not be as hard of a sell as he initially let on.