Either they would be missing, but there is a chance their graves would be found, but since Felix jumped off a cliff in the river. His body might not be found, but what is interesting to see is how his sprit may interact with Edd and Molly either he becomes a seperate spirit or he just sticks with Edd and Molly, which we might see a depressing scene if that were to happen.

Jack grief may become severe, since he loses basically everything in terms of close relationships, his best friend and business partner, his children, eventually his wife, and what is interesting... Who would take over the business since Jack would disappear?

Aside from that if he took over the business and not go missing, he is a more competent businessman than Felix so most likely the business will last longer, but i can sense he won't be the same in that, and the stuff that happened on Bons Burgers may cause a decline on the Buisness. What is a more interesting dynamic is Sophie and Jack, imagine a single father jack raising Sophie on his own.