First, commonly used features aren't deprecated frequently. Second, you'd get a warning at least a year in advance (the more important feature -- the longer the warning). BTW, note that when something is removed from mainline, it is no longer maintained in Updates (because there are no more patches to the component to backport), and so it's not supported in "free LTS" offerings. If you want to continue using removed features for a few more years your only option is to buy long-term support.

good point