I think it's the right moment to acknowledge that Epic Games handled discontinuation of Unreal series well and responsibly [0] and how standalone servers were good for community.
* When GameSpy announced shutdown, patches were released to use Epic released the "post-GameSpy" patch, replacing the GameSpy servers with Epic's master servers for Unreal Tournament 3 [1]
* Older Unreal series games later were transferred for maintenance to OldUnreal [2], and also made free.
At the same time, they are not open source, nor source available. So, there is an entity, that owns the code and maintains it, without the hassle of opensourcing it.
This is because the series have a strong community, which was in large part formed because the standalone servers, prior to algorithmic matchmaking, allowed people to gather there and learn to be social to each other and learn gaming etiquette. You had to play strategies for repeated games and be civil to others. Modern matchmaking strips us of that - you play with others once and go separate ways, so you don't have to deal with consequences and can use one-time game strategies, which leads to poor behavior and less enjoyment. Yes, you had players of drastically different skill levels on the same servers, and that was a good thing. Skilled players could teach newbies, newbies could learn the gaming etiquette and see what's possible, instead of boiling in the same pot with others playing completely different games than on the other skill levels. You had the core game and the social game on top of it, now we are all alone in our rooms interacting with strangers we will never see or play again with nor against.
Maybe Epic is not the best or the most loved company (compared to Valve) but I respect, that they understood that "this cow has gave us enough milk already", and could part ways with it, leaving existing community satisfied.
[0]: https://www.epicgames.com/unrealtournament
[1]: https://store.steampowered.com/news/app/13210/view/291772582...
[2]: https://oldunreal.com/