Minecraft is a rare bird that lets you download every single public release (that was archived) all the way back to the original test builds. I recently re-downloaded 1.14 to play a unique seed that only loads all the features correctly on that version.
And when you play Minecraft, you download the entire game as a .jar file to your computer and it stays there, even if you upgrade to a later version. There are third-party launchers that let you load those .jars and play without logging into anything.
So, it's up to you whether or not you tow the company line and use a Microsoft account and the official launcher or just download some fan-made software and run the old versions forever.
I recommend anyone who lost their Mojang account to just dig out the latest version downloaded to their computer and run it through a custom launcher, or look up instructions on running the game without a launcher.
(This only applies to the Java version of the game, but that's the best version anyway because of features and custom mods. Playing roms of the console/mobile games requires modding the appropriate system and that's a lot more involved.)
There is a reason they deactivated the accounts, but it doesn't justify removing the ability to migrate at any time. For those interested:
The old mojang accounts were not secure, and there were millions of accounts that could be accessed without email ownership. This created a grey market for cheap Minecraft accounts. These cheap accounts were almost exclusively used to cheat on non-cracked servers, which sucked for a lot of players who did competitive Minecraft games on servers. The migration did fix this problem, by requiring access to the original email or answers to the security questions. Migrating your mojang account also gave access to the windows 10 version of the game. It probably should have been allowed forever, and I have no clue why they didn't.
I do wish I could say it will pass, but the ability to sell someone something they already purchased is the holy grail of sales. This isn't going to go away, and the EULAs you agree to ensure that it is entirely legal.
The only way to fight back is to vote with your wallet - sadly in monopolies that isn't really an option.
I got locked out of my now 8+ year old account because I had set it up with an old ISP provided email which has since been deactivated. I can't migrate because I have to verify with the email and I can't change the email without setting up security questions, which also requires the email. Support can do nothing.
I'll tell ya more, if you read hardware license agreements then you know that even with hardware you don't "own" anything, you just bought license to temporarily use it, i was shocked back in the day when i read license agreement on my iPad 4 in 2013, there was point about it, that i don't own but only bought temporary rights to use it
I do not have any of GAFAM (Google, Apple, Facebook, Amazon, Microsoft) accounts and this is nice "achievement" to have in life for me.
Maybe if I would need them for something important like becoming a video creator, having to publish an Android app for a company or promote my buissness on social media I would create one. But for just one game it's a pass for me. The most important game in my life, but I have grown up and do not play it anymore.