I don't know if this exist or not, but it doesn't hurt to ask.
Sometimes, few people I know (and maybe I don't know) change their username without any some sort of notifications, unless going to their profile first. In order to find their profile page, you have to know their new username. So my idea is that if you type their old username in the user search bar, you should be able to go to their profile without any problem even if they already changed their username to something else.
If there's any problem against this, I would like to know.