Warning: Contains spoilers for Arrow 4×08, “Legends of Yesterday.”
Granted, DC’s Legends of Tomorrow needs a Big Bad. However, that does not narratively explain Malcolm Merlyn’s bid to resurrect Vandal Savage at the end of Arrow 4×08, “Legends of Yesterday.” Merlyn probably thinks he needs Vandal Savage or his knowledge in order to reconstitute the Lazarus Pit. He does not, however. The current Ra’s al Ghul has all the tools he needs to deal with the Lazarus Pit on his own.
First, Merlyn has the remaining liquid that the previous Ra’s devised to neutralize the Lazarus Pit. That liquid is, in fact, liquid. It is a tangible substance that could be tacitly reverse engineered. The former C.E.O. of Merlyn Global Group would have no trouble finding a facility through which to perform the analysis. Indeed, if Merlyn were feeling particularly perverse, he could employ Votura (as he did with Thea) and use the S.T.A.R. Labs crew to do the work for him.
Second, even if the analysis of the liquid shows that Nyssa’s father mixed magic with his chemistry, Merlyn would still have no need to despair. Before the Age of Science, there was a magic-heavy branch of proto-chemistry called Alchemy. The previous Ra’s undoubtedly studied this discipline, famed for its pursuit of the Elixir of Life, in order to determine how to neutralize the Lazarus Pit — the actual Elixir of Life. Merlyn would have to roll up his sleeves, put on a pair of cotton gloves, and locate the same books on Alchemy that the previous Ra’s must have used. Those books would logically be found in the League’s extensive, millennia old library.
Third, in addition to the search for the Elixir of Life, alchemists studied how to transmute matter into other forms of matter (i.e. lead into gold). Alchemists accepted, as do the scientists that followed them, that matter cannot be destroyed; matter can merely be changed. Ergo, the Lazarus Pit has not been destroyed; it has simply been changed. There is still a “magic hot tub.” The liquid inside it performs a different set of functions. If he has his wits about him, Merlyn would not limit his enquiries to what the Lazarus Pit used to do. He would also explore what the Lazarus Pit can do now.
In conclusion, Arrow’s writers are missing interesting, internally logical story opportunities out of fear of the Lazarus Pit becoming a deus ex machina. Unfortunately, that fear has driven them to turn Merlyn, himself, into a deus ex machina. He will employ hand waving methods in the service of a different (albeit interconnected) show. He will resurrect Vandal Savage in order to justify actions Merlyn would take on his own if Arrow were an independent narrative.