If you actually use and care about the software this shouldn't be an issue. Unfortunately to run even a small business where a niche product only needs to be bought once it needs to be way more expensive than that licence was.
I have a lifetime licence to my text editor and I've used it every day for over 10 years, wouldn't have an issue if the creator changed their mind about it and actually the community has asked them to so it could be supported but they were not interested.
He sold it with a lifetime license. Secretly changed the license on his website and then years later stated that he was breaking the license and HIS WORD.
That said, he could easily say the last update was the end of mIRC and then release the next patch as mIRC 2 with a new license. Much like how Sublime Text works.
I have a lifetime licence to my text editor and I've used it every day for over 10 years, wouldn't have an issue if the creator changed their mind about it and actually the community has asked them to so it could be supported but they were not interested.