Thinking about the gaming magazines I used to read as a kid in the '90s.
I remember those fondly.
It would be an insanely short-sighted practice to not keep masters of these publications forever, no?
You're talking about capitalist organisations here... there's nothing about them that isn't short-sighted.
The raw files probably take up a few CDs’ worth of space for the entire run of the magazine.
Nope... just one cover page probably takes something around 300mbs at a minimum and could be a whole lot larger depending on the quality of the imagery used (if I remember my time in the printing/publishing industry correctly) Storage of already printed material in those days was always an afterthought.
Do they retain the files forever?
Highly unlikely - a lot of the storage just got dumped at one point or the other since there was really little reason (profit wise) to return to anything at all. There might still be an old Mac sitting around somebody's garage or backyard which still contains the stuff, but I won't be holding any hope out for that. There's always the chance that some employee still has the disks somewhere (you'd be amazed at how necessary it could be have proof that you actually did work somewhere and actually did work on this or that specific thing - the bosses were notoriously petty), and I suspect that's how a lot of stuff ends up on places like archive.org.
The corporates themselves don't give a shit - as soon as the profits roll in, it's all expendable as far as the overpaid geniuses in the fancy offices are concerned.