Items And Loot Archive

What happens once u finish the YT-2400 quest and u havent gotten the jedi master robe or maybe the bounty hunter rifle that doombringer drops what then can u redo the quests and try to get it again or how does that work i know for one i would very much like the robe and also the new MBH rifle not the crappy reward one but how do i make sure that i can get it

this has just been on my mind much lately since i never seem to be able to loot anything good and i would be really sad that if i bought an expansion where i cant get the few things i mostly want