You know this isn't the first time someone has reported on having disk scratches on their mario kart 8 discs, also don't use your Wii U vertically anymore if Nintendo gives you a replacement... and I'm pretty sure there's a knife or something hidden in your Wii U for it to make that bad of a scratch (Also, check your other discs to see how they are).
actually, my game disc's top side is slightly torn, not scratched. so, do you think it is still safe for me to play my games?
This indicates that something inside your Wii U is scratching the heck out of the top of your discs. You need to contact Nintendo about getting it fixed if you're still under warranty...they should repair your Wii U and give you another copy of Mario Kart 8, imo.
If i dont fix my wii u, will my game discs still damage my console?