forever is not a time scale that software works on. without serious effort you cant run most programs from 15 years ago that you own outright, even if you have a floppy drive still. do you?
Actually these days, it is childs play to do this...you can easily and readily set up a VM (Virtual Machine) to run any particular OS and application for it, using things like :
Virtual Box: (FREE)
Parallels (mac only)
And many of us are trying to vote with our wallets. Other companies, MS for example, have tried the rental software model, and so far (thankfully) have not succeeded.
It may work for some, but many out here prefer to have a choice to rent or buy perpetual licenses. I think we may be seeing Adobe keep extending these "deals" because the uptake and acceptance of this model may not be up to what they're expecting.
I say good....maybe they'll change like other companies that have tried this and go back to at least also offering purchase rather than rental only.
ps. Actually yes, I do have USB floppy drive at home, just in case I or someone I know comes across some old files on a floppy they need to retrieve.