We have a fair bit of code in production that was written over 20 years ago. It just works. It has gone through strings switching from 8-bit to Unicode (16-bit) with hardly any modification.
We upgrade every year or so, and in almost all cases it's smooth sailing.
Delphi has been quite good so far when it comes to long term maintenance.
First they deprecated the bundled DB bindings, after hyping them to hell and back; then the bundled report generator. We had more than a million lines of code depending heavily on those.
Proprietary, with almost full sources to the standard library, however. There is indeed a bunch of half-assed stuff, but that's easy to ignore. In general, Delphi moves slowly and hardly ever breaks backward compatibility. Only the transition to Unicode in D2009—oddly not mentioned in the article, along with generics—was a little rough. Apart from that, decades old code keeps compiling/running without issue. It's mostly third party components needing updates sometimes, especially if they're shipped as compiled units or integrate with the IDE.
Mate I've got a project whose first lines of code were struck back in the 80s in Turbo pascal. Your "continuously deprecated" argument doesn't hold a lot of water from where I sit... In terms of actual language features/changes that have caused deprecated status, those are very few and far between. Maybe some VCL database controls, for sure it would have sucked to have built stuff relying on interbase, but that is not a language/compiler feature, that was CodeGear EOL that particular project (I had to manage the exit strategy on one of our projects where it relied on that crapware)
Even library developers are pretty good at pumping out versions of their libs that have support for even Delphi 5. I know of at least 2 people who are still doing windows dev on Delphi 5 or maybe 7, I can't recall.. the very definition of "from my cold dead fingers".
Suffice to say if you were one of those real hold-outs, not updating to the latest.. you wouldn't have generics, dynamic arrays, lambdas/anonymous functions, and you would probably struggle to grab much code written in the last decade and compile it straight up.. but that would probably be the case for a number of languages that have had core features added to them over time.
The fact that the system is proprietary certainly is an issue, but every install always ships with all the source code of the RTL, VCL, and clear instructions on how to compile it with a "you're on your own now" sense of adventure.
