When You Beat the Last Boss of a Game

It's not limited to those two, it's very common, generally the norm, not having a postgame state when the stakes are too high. You've got two choices :

• let the player come back to it after you beat the big bad, so you have to create new interactions to try and reflect that, and not change the world significantly so all the stuff that's left to do is still available and makes sense. It often feels like saving the world achieved nothing.
• show in the ending that the player actually achieved something big, to the point coming back after it would not be the same game, basically.

How would you explain returning to BotW after killing the source of all shit and still having hostile guardians and blood moons resurrecting monsters?

Looking at you, BotW and TotK.

are you fucking kidding me? I'm finally getting around to properly playing BOTW and I assumed you could continue the open world post end game.

I don’t remember which boss it was but when I was first playing Sekiro I finally beat this boss and the motherfucker comes back to life in a renewed form. Maaan it pissed me up so much for a second, then I got scared but then a bit after that it was actually a good challenge

It felt really good repeatedly kicking the part of the boss that took me so long to beat at first.

More like Super Metroid