My friend and I were talking yesterday, and the portals might take them back in time. But then we started talking about what would happen if they time traveled, and let me tell you, it wasn't pretty.
First of all, there would be two of Jesse, Lukas, and Petra. That could probably create a paradox. But what happens if Reuben doesn't go into the Witherstorm? When Jesse drops the sword, who brings it back to him/her? The answer is this: Nobody. Jesse would die, and Petra would either be dead or have amnesia. The world would stay a living hell, and the Witherstorm would probably eventually wipe out humanity. So there we have it. Reuben has to die, or the world would be destroyed.
My opinion, (Hey I said my opinion so no hate pls) is that you know they know what will happen next so probably that will happen you know but they will really need to leave that portal cause you know, probably the portal closes, so you know, still.