Apparently Miura told Mori pretty much everything that was planned, at least in broad strokes. The statement also indicates that it was pretty well fleshed out too, and that Miura hadn't much deviated from those plans in the decades of making Berserk. Assuming this is all true (since the two of them were the only ones party to the discussions) then we are likely to get basically the story Miura intended.
The art from the last comic and the new teaser are obviously not drawn by Miura. The team doesn't perfectly have his style down. However, in a way it's alright because we know that they aren't him anyway, and he pretty much kept the integrity of his art until his death, as he wanted. The replacements aren't him and don't look like his work really, but they are all still excellent artists in their own right. It's not going to fully be Miura's Berserk, but it will be Miura's story carried by his apprentices' art.