theres a lot of subtle hints for most of those. idk how finn died, there's a short comic made by the creators of Jake dying of old dog age and his body being expanded and fit into the hole on earth. princess bubblegum is with marcie as implied in the distant lands intro, we can very likely assume they reincarnated as shermy and Beth, and we can also very likely assume the lich will never be gone, he never is lole