Possible rejuvenation spoilers:
In rejuvenation, reborn is cannon. We know this because both Adrienn and Aya go to the region. Also there is a 5 year difference between the end of reborn's storyline and the beggining of rejuvenation's story line ( iirc jan confirmed that ) and Aya said that the MC reminds her of the current reborn champion who fought Team Meteor. Also we know it's not Fern because she also says before or after you battle her, that she met a Grashole and that he pisses her of because "If you are good, you are good.Don't be a douche about it" ( or something like that). This is a refernce to when Fern beat her and then made fun of her because she fought in doubles.
So both Fern and the MC are known and rememberd for their perspective roles in the Reborn region.
So i don't think something like this will happen.