And no, you won't have any warning they are going away, unless you are an insider. They DO go poof in the middle of the night.
Outside of the financial industry, it is very rare that a major corporation suddenly and without warning shuts it doors and leaves all customers out in the cold.
To point out a good reference, Adobe took down their activation servers used in CS2. So they put up new software packages and keys for those who would have been unable to activate their software.
Honestly, anyone afraid of loosing their edits and work in lightroom, when you upgrade, keep that install file around on your hard drive with all your photos. At any time, you can rent/borrow/upgrade/reinstall/virtualize a PC or Mac computer, install the 'dated' version of Lightroom and get a 30 day trial. Open your existing library and do a mass export of everything to TIFF.
Still afraid? I can't help you. Adobe is in an odd spot right now. Their tools are the industry standard. We as the creative public want tools that make things easier and allow us to work quickly when dealing with huge amounts of data. The technology isn't cheap, programmers aren't cheap, and theirs is a company that didn't have a reoccurring revenue model. Creative Cloud gives them revenue monthly, to help level out the stock price, and keep income and expenses balanced.
If you make your living with Adobe products, $600 / year is a cost of doing business. You write it off with everything else. The catch is those who only dabble in Adobe products, who aren't willing/able to spend the extra money. I don't see how Adobe is expected to separate those two user types without being abused.