It's not the end of anything meaningful. Sony's just selling off their stake in the company. Square-Enix isn't going to suddenly stop producing titles for their machines; that's [censored] stupid, especially in today's climate.
And FFX is one of the last "true" FFs because XIII+ is nothing but narrow halls? Well, Spira might not have consisted of hallways, but it might as well have; just about every single dungeon in the game is one narrow path with few, if any, branches.
If you don't innovate your cash cow franchise, it grows stale, people get bored, and eventually move onto other things. Particularly when a competitor releases something better. There was once a time when Square was the go-to company for when you wanted to experience something that told you an epic character-driven story with a lot of pan, flash, and cinematic flair. That's no longer the case, though. Not necessarily because Square's been failing to deliver on that, but because everyone does that now.