The universe is already done for. The space outside Mavuika's sky hole and in Skirk's video is red because everything is redshifted, ie. the universe is expanding in all directions. The end result is the heat death of the universe. Surtalogi's pet, the whale, is a symbolically a black hole. He is using it to hoover up whatever matter is left in the universe so that he can try to reboot it. The Heavenly Principles has been trying to maintain a force field around the world to protect it from the cosmic entropy that has taken over the rest of the universe, but it is doomed to fail, and soon. Surtalogi said fuck that and is out there trying to figure out a way to fix it by finding another Descender. The Abyss in Teyvat is a reflection of the chaos outside the world. Its nature is to break up out of the ground and consume Teyvat just like the nature of the cosmic chaos is to break in through HP's barrier and subsume the world.
>source: just trust me