archive.org, of course, has partial copies of some of these -- but it often seems to have trouble with comics and is usually missing years and years of content as a result.
Part of my motivation is similar to your worry that these things will disappear forever, despite having been a huge part of our culture. And I figure one of the best ways to get help on archiving comics is for people to complain "hey your site doesn't do comic X" and then I know that it exists and can get it into the system for crawling.
I know saying "hey I'm working on it" isn't much better than "hey I thought about that too" but if you're interested I can attempt to let you know when I get far enough to put it up on the web instead of my workstation at home.
Obviously, re-hosting web comics is a murky, at best, territory, but this will easily allow local only access for your personal benefit.
I think rehosting is pretty bad, copyright infringement at best and not very nice to boot. That's why I decided that cropping and thumbnailing would be the way to go; enough of a picture to let someone say "yeah I saw that one already" but not so much that they don't go to the artist's site to see new comics.