Yes. After Corypheus "dies" in Legacy you have a chance to loot his corpse and can walk up to Larius/Janeka at your leisure. However, I don't remember if you get a similar chance in Mark of the Assassin.
Regardless, if you use your sibling again during the game's climax, they have the same gear they were wearing the last time you saw them, so that gear you gave them isn't isn't lost forever.
Mountains. Cold. "Let's bring Dorian!" It's good to be Champion!