Yes, it can. They could give her a new E ability or ult that’s a large burst heal or something with a similar animation to rez, with the idea of “bringing someone back from the brink of the death” like she did with Genji. They could even keep it named Ressurect, but just change the way it functions so it’s activated before someone dies and not after. The Devs have already said that Rez is purely an in-game mechanic, and not actually in her lore. And Jeff did say in an interview that they would be sad to remove rez, and want to try to keep it. Key word: try. It doesn’t seem to be working very well.
Except Mercy 1.0 was a troll pick because she didn’t have impact. She had no E ability, a burst ult that felt cool to use with shiny visual effects but wasn’t actually good enough to warrant playing her over any other supports, and her old GA made her pretty vulnerable against dive. It can be argued that she had less impact than current Mercy.