You can't always come back. I would say most things give you 2-3 chances and the order doesn't matter but certain decisions are a one time chance only and if you miss it, it's gone. And if you miss those 2-3 chances, things are also gone for good.
For weapons the best example is during the "Prologue". While you are still on the Nautiloid there is a strong enemy with a burning sword. If you play as "intended" and ignore the enemy, you won't get it. And there is no option of getting it later (to my knowledge).
Then there are a lot of other decision where you aren't sure of any long-term consequences. During the first 3-4 hours this bothered me and I did a lot of reloading trying to find the "optimal" way. But by now I embrace it. I finally have a solid idea behind how my character would act and just go with decisions inline with that. And I will have multiple play throughs of the game almost certainly.