With the Sentinel League coming to a close soon, the Grinding Gear Games team has addressed the community question about whether Sentinel League will become a part of Path of Exile’s core mechanics. The answer to that is “no, for now”, but there’s still more to know.
Sentinel League will end in a few weeks and all of the Power Cores and Sentinels will be deleted. However, the team has gotten a lot of questions about whether or not it would be integrated or returning, so in their response of no, for now, it does leave the door open. They’ve also explained just some of what it would take and why it’s not going to stay right now.
“The league would take some changes before it would be appropriate to become a core Path of Exile mechanic, and while this is something we're interested in looking into in the future, it's not the time now.”
That said, while Power Cores and Sentinels will be deleted, Recombinators won't drop but you will still be able to use the existing ones in Standard until eventually they’re consumed and become scarce.
Effectively, they are looking to bring them back in the future considering the crafting options Recombinators opened up. If they do bring them back they say that the ones that still exist in the game may change their functions, but as always, the team will let the community know beforehand before such a change would take place.
So while the team won't be integrating Sentinel League in the core game anytime soon, The door is definitely open. For now, if you haven't completed your challenges in the league, you have a few weeks left to get them all done before the next update arrives.