To think Elena and Damon are going to remain together or be on/off throughout the rest of this season and the entirety of season 6, to result as 'endgame' - is just ridiculous. That's quite obviously not going to be the case, aside from the fact we've been witnessing how their relationship is no where near functional…

Katherine is not coming back. The writers put her in hell for that reason, because it confirms her not returning, whereas placing her on the other side would always leave 'a return' optional.