So as an adaptation this finished the whole WN which was 39 chapters (and LN which only got 1 volume in 2018), the end of this was advertised as the completing part 1 of it, but the thing is that it been 2 years since this one ended, and 5++ years since the WN finished, and who knows if that part 2 or whatever is even happening, author work of focus for years been Reincarnated Aristocrat anyway
Unless they lean all the way into "the alchemist demon lord really doesn't care about anything other than his research" an open ending is probably the best option.
They killed off the strongest hero, his replacement, and both their teams; Rick is going to keep churning out SS-rank monsters; and never mind what happens once he starts synthesizing
those together. The power balance is already completely gone, and with it, any hint of narrative tension unless, again, they lean into some sort of slice-of-dungeon-life genre.
Maybe introduce the biggest bad, whatever god or demon lord-lord is making the dungeon cores and come up with some reason that Rick has to do something about it anyway.
But I'm not sure how much longevity any of those storylines have.