My external Wii U hard drive broke last year (literally a hardware failure, rendering the disk unreadable unless I opt for a costly and risky recovery method that would cost several hundreds of euros with no guarantee of full recovery due to the very specific formatting needed for the Wii U).
I lost everything. My Wii U is dead since, I am still mourning.
120+ hours in Xenoblade X, with me just starting chapter 8 (I loved mucking around, story progression came last for me in this game). I had 4 mechs.
80+ hours in Zelda, I never bothered to go to Ganon's castle, and I guess now I never will.
Completed save file in Tokyo Mirage Sessions, waiting for me to return to New Game+! I mean NOT waiting for me anymore.
Mario Kart 8 with even the gold tires unlocked already.
Worst of all, because absolutely irrepairable (unless hacking with a game shark or whatever): My Wii mode save file from The Last Story with all weapons from the now completely defunct online multiplayer unlocked.
I can't go back at all. Every time I boot up the Wii U and my home menu is just EMPTY because everything from my hard drive is gone, I immediately turn it off again.
My 400+ hour Splatoon save is still there at least. But yeah, haven't touched my Wii U since. I can't.