I'm struggling to think of a comic where this would be necessary.
Because if it's an old webcomic, like say, Gunnerkrigg Court or Scary Go Round, most of the ones that had decent art, the creators kept higher resolution files because they used them to make print books (or maybe they even have the original trad media pages.)
The creators who didn't, it's usually because they were really inexperienced artists and so even if they got famous and really good later, they're not that bothered to give it an HD remake. Like really, even if somebody thinks Giant Days is amazing, I don't think they'll go out of their way to get Bobbins in high def...because it's really not as good as Allison's later work.
But outside of that.... 800px isn't that small when you consider that uploads on Webtoon as 800px wide, and Tapas 940px. These comics are acceptable to look at on a screen, even if they're not perfectly crisp.
If I was going to redraw an old comic, especially one from as long ago as the era of "don't make your pages more than 800px because a lot of people's monitors are still 800x600" which was... geez, early 00s? believe me, I would want to redraw them for more than just the resolution, because my composition, colouring, anatomy, perspective etc. were so much worse back then. I'm not sure why anyone would want those comics even with the art improved though... because the story and dialogue was also very bad. I don't think AI could really help with all that. I'd prefer people just read my newer comics rather than seeing them digging up the terrible old ones off Drunk Duck and scaling them up with an algorithm.