It will not be undone, just like Mantlo's stuff hasn't been undone almost half a century later(in fact it was expended upon by some other writers like PAD and now further expanded by Ewing), just how PAD's run hasn't been undone, just how Paks run hasn't been undone, etc... Literally the only time i know of a Hulk run being actively undone was the Bruce Jones stuff and that's also because it was wildly unpopular among readers and other writers so PAD just came after and established that most of it was just a dream Nightmare put Hulk in. Other than that can anyone show me what has been undone from Hulk? Was Maestro scrapped away? No 30 years later the character even has his mini series and was even mentioned as Hulks CANONICAL future in History of the Marvel Universe. Was Planet Hulk/WWH undone? Nope it constantly gets referenced to this day. Even smaller and less popular runs have gotten their mentions like Doc Green and the fallout of that was referenced multiple times in Immortal Hulk as far as issue 34 were Leader merges with Gammon the rogue A.I that escaped Doc Green, the only way for something to be undone is for it to be very unpopular or forgettable or if God forbid someone like Bendis came along and started writing the Hulk(which luckily at this point is an impossibility), other than that Ewings legacy will be safe.
Now is it possible that 5 years from now Hulk will no longer be "immortal"? It's possible although highly unlikely considering Ewing painstakingly went back since Incredible Hulk #1 to establish Hulk was always immortal and even PAD himself has hinted at that idea back in the 90's and even in his current Maestro run not only did he reference the Immortal Hulk run by saying he used to be called "the Devil" he even outright said Hulk is still immortal, so other than that i can't imagine any writer even attempting to retcon/undo anything Al did. The run has been a huge critical and commercial success, I've seen a dozen writers from Marvel to DC praise it. Even writers that have expressed their desire to write a Hulk book some day like Scott Snyder, Donny Cates, Jeff Lemire, etc.. have said they loved what Ewing was doing even calling it one of the best books out there.