As long as you purchased them, they won’t go away. If you bought it, you own it.
Image Comics Director of Business Development Ron Richards explaining why “For the First Time, You Can Actually Own the Digital Comics You Buy.” I bought the latest issue of the Walking Dead (you know, for research…) and was never confronted by any Terms and Conditions limiting my rights to use the files as I would any other computer file that I own.
Now, under the ReDigi decision, you still couldn’t take advantage of many first sale rights because the comics are digital files and can’t be loaned or sold without copying. (Section 109, where first sale lives, only provides owners with an exemption from the distribution and display rights, not the right of reproduction.) Still, DRM-free files you can download and keep is one step closer to real ownership, and a step away from merely licensed access that can be revoked at any time.
IMHO, a library could buy these digital comics and put them on an e-reader device (an iPad, e.g.) and lend the iPad with the file installed. A little wonky, but it looks more like real circulation.