If "In the beginning" Cas told Dean "Destiny can't be changed Dean.All roads lead to the same destination" when Zachariah sent Dean to the future at "The End" he won't be able to change Sam's decision agreeing to Lu?What do anda all think?

Cas didn't want Dean to change his future so he left out important information that would make that possible, the whole point of Dean going back in time was to see why Azazel came after Sam and what he did to Sam. Zachariah wants Dean to change the future, so when he sent him into the future he made sure Dean had all the information he needed to change it to try and convince Dean that sejak saying yes to Micheal it would prevent Sam from saying yes and stop the apocalypse. But what he didn't count on was Dean realizing that sejak sending Sam away he was just making it easier for Lucifer to convince him into saying yes.