Gods cease to exist if no one (human) prays to them or believes in them. His only lifelines were his "father" and Hiyori. With both of them gone, he doesn't exist any more. Yato was the personal "God of calamity" of his father.
Since his father was "immortal", Yato continued to exist. This is why Yato was so determined to get his own temple. He didn't want his existence to hinge on his father.
As to if he comes back or not, we will see since Hiyori is alive, but it's possible that when a god's total believera drop to 0, that's it. Even if they are prayed to again.
There's a good chance he might get reborn since he has his own little shrine (it is in Hiyori's house) and a small tent-space in Heaven.
Wait so.... Is yato dead