I'd suspect that at least the Elite will continue to be serviced as long as the GT, as the control board seems the same for the most part with some minor differences and changes in external controls. Same box. Same face plate (with the controls difference). Same battery system.
Far as older electronics go, if an electronic gadget is going to fail it usually will do it within the first year or so of being made, as that's when a borderline component, cold solder joint, or loose wire is going to show it's self. Once it gets past it's "teen" years it should be pretty much trouble free, providing it ain't abused by getting it wet or damp, or letting it bake in the hot sun. I've owned a lot of machines over the years, most of which bought used to save a few bucks, and I can say that I don't ever remember having one fail on me. Never worried too much about warranties. Even when I bought new I have to admit I hardly ever sent my card in. Just didn't worry too much about it, having never been bit by a bad detector. Well, I take that back. Years ago I bought an old 80's era Bounty Hunter (2nd machine, bought used in the 90's), and it ended up going bonkers on me after a few weeks. At $40 for the cost of buying the thing, I guess I got my money out of it, and in fact I did because I dug a ton of clad.
Think of it as buying a new car. Usually in the first year or so is when it'll end up seeing the dealer to fix some bugs. Once it gets past that it's pretty much home free most times. At least that's been my and my families experience with new vehicles.
You hardly ever heard of a Sovereign breaking down. I have heard of older models having a few of the capacitors go bad in them, but that's an easy fix if you know how to solder. Used to be capacitors (not just on a Sov) were made of a insulating material that would break down over time between the layers of the plates. Not sure but I suspect that issue has been corrected in the last 20 years or so maybe.