A Lazarus pit seems too obvious a solution, and I would think the presence of magical resurrection in the Flash/Arrow universe would cheapen the stakes. We've been teased with the possibility of the Pits, but I think that's a deliberate mislead. I mean, if Malcolm and Ra's have access to Pits, Nyssa would surely be aware of their existence, but then one would expect Sara to have been tossed into one by now. I mean, when Sara initially died, I thought she's come back right away, but the League's reaction to her death seems to indicate that there's no cure for dead in this universe.
That said, it'd be nearly impossible for Oliver to survive what he just went through. He's basically dead in three different ways right now: A crushed windpipe, a fatal stab through the chest, and the fall. So... though I don't think Lazarus Pits will be used, I don't have any better ideas.
Also, while having both Flash and Arrow face their greatest enemies this week somewhat explains it, I was a bit bothered that neither team contacted the other for help. Even if neither hero was able to help the other, I would think the request would at least be made. Oliver has proven capable of handling Barry in a fight, which would make him a valuable asset against Reverse Flash, and Barry can potentially trivialize a fight against a "mortal", which would make him helpful against Ra's.
