That idea shouldn't even be entertained and would be a total farce if they go ahead with that.
They have reserved a slot on Friday if it's still a no go tomorrow, or they can move to Vaires-sur-Marne as a back-up location if the Seine water quality isn't getting any better.
I just don't understand how they could hold on to Paris as its location so stubbornly when it's been fairly obvious that this scenario was always gonna be in play. There are other (water) sports which are being organized in Marseille and Tahiti as well, so wouldn't have been the end of the world to have the triathlon in Nice either. It's all nice to envision one of the most iconic Olympic sports in the heart of Paris but the athletes should always come first and if no guarantees could be made, they should've moved its location beforehand.