I have to disagree here. While it's (very) unfortunate the volume didn't get a cover illustration from Miura, episode 364 itself definitely bears his stamp. And I think comparing it to what we got with 365 & 366 makes it even more obvious. They shouldn't be lumped together!
Well, I'm being a bit facetious there, and it's true practically speaking that you can tell he definitely designed and had almost completed 364, and that's basically how I saw it. But it's also true that's where he left off and his assistants had to take over, and this reclamation project sort of began, which does color my view of 364 and it's place in all this a little. If they'd just capped it off there, put a period on the end of Miura's sentence, fine, but in retrospect that was the proof of concept for this continuation and "where it all began." It was at the very least the seed, and I guess it's best to see it as a tribute to Miura that his team was able to do this at all.
Anyway, it's obviously a really special and singularly unique episode given the circumstances of its completion, but it's also the transition episode and the biggest argument for this creative team continuing, if not the deciding factor. Hell, 364 is basically the hugest possible cliffhanger ever to dangle out there, and the worst stopping point, practically
begging to be continued. If you were going to let sleeping dogs lie, you leave it at 363, the last episode Miura completed and published in his lifetime, and close the book.
As for the cover, that's different. I would have preferred they used ANY leftover artwork from Miura, whether it was context appropriate, just another shot of Guts, something comprehensive to commemorate the whole series, something unfinished to acknowledge the circumstances, or fuck, on that note even just a black box or blank cover. Now, again, in retrospect it's hard not to wonder if the decision they made wasn't in mind of the transition to the new team. See, this is why I have to stay positive about all this, otherwise, I'll be a very cynical, unpleasant guy.