I was playing Borderlands: The Pre-Sequel (Handsome Collections, PS4). I defeated the final boss and the end credits started rolling. I watched these for a while (the accompanying illustrations were cool and filled in some of the BL story). But I had something else to do. It didn’t seem possible to skip the credits (I’m sure I tried pressing all the buttons on my controller). So I quit the game while the credits were still rolling; i.e., I closed the application using the PS4 operating system.
When I next played the game, I discovered that all the loot I had collected from the final boss (including at least one legendary) had disappeared from my inventory, and the last stage of the final story mission was still incomplete. I thought this meant I would have to kill the final boss again (not the end of the world). But when I went to its location, it did not respawn. In effect I have lost the opportunity to receive any loot from the final boss.
So my advice is do not quit during the end credits!