Of course the fact that a company that no longer exists can't support such a configuration doesn't matter because they aren't there anymore to care about any of it.
If I was the company though I would make sure that them providing the new source would be part of that $20k though or an agreement that when he no longer offers his services personally, regardless of whether he sells the company or not, that he will also release the source code to them if they are unable to negotiate for it upfront.
I think that would be fair and fulfill both parties concerns.
I personally prefer open sourced solutions as well, but in business that just isn't always practical.
I got into free software relatively early in my life and it was like watching a parody film before the original.
In most cases, the limiting factors for lifespan were: 1) Inability to get replacement hardware 2) Inability to find anyone who can understand the source code.
There's really no way around issue #1. Having the software source doesn't really help that much because most of the time they'll use "migrations" every 10-15 years to rewrite the code using updated understanding of how they want the plant to work. Kicking off a SCADA upgrade is used as a wonderful convenient excuse to drive a lot of meetings/paperwork processes to define "How can we improve safety, improve reliability, make life easier for the human operators, etc?"
Nowadays, the thing time-limiting many SCADA installations are licensing for Windows LTSB and PLC/DCS vendor software. Often times newer versions will require new Dell/HPE servers for compatibility. It's expensive, but also not expensive enough to focus on changing.
The main point is that while licensing artificially limits "longevity" of a machine, closed-source does not. Instead, unavailable replacement hardware limits "longevity" more than "closed source" does.
Just look at the price of used serial consoles with Sixel support.
Some hardware can be replaced by software... but not all of it.
I really love the nostalgia this kind of hardware stirs in me, but I am glad I do not have to deal with that kind of trouble. (A few years ago, I read on another forum about an IT guy getting a call on the weekend from a desparate customer looking for an HDD using some standard that predates non-S-ATA... MFM, I think?)
We expect minimum 20 years from PLCs, and unless parts become unavailable or failures too frequent we would generally go 30 years before replacement.
The PLCs are great, it’s the damned computers and their operating systems that keep needlessly changing our working system.
So we virtualize and air gap.
That's my gripe these days, long term used to be 20+ years. You can still get DL400 series PLC's from Automation Direct (rebranded Koyo) which are from the 90's. Now I see many embedded micros and processors advertised with 10 year long term supply. To me long term is around 20 or more years, basically someones career span. And dont get me started on all this industry 4.0 PC based control crap. Not everything needs millions of lines of Linux kernel to turn a few io points on or off. And the bloated systems that these platforms utilize is nauseating.
Heck I think there's a lot of value in an emulator for old device drivers. Who cares what the source was when you just execute the black box in a highly regulated sandbox? (Note doesn't work for some medical software). I think medicine and astro / aero are the few places that would require full decompilation of an original driver.