Well, I guess Ubuntu Advantage would be a good place to start if you are willing to pay for services. What you're really asking for is a snapshot of all the repos, which is no different than mirroring, which you can do yourself for free.
It's not as if the images are destroyed, it's just security updates cease after a while, at which point you would have to scramble and perhaps confine it to a VM with only the bare necessities open to the world, even then, that's a massive headache.
Everyone's apps grow roots, you'd be better off to begin the effort now to port whatever it is you're dependent on forward, perhaps even package it. Good luck.