Probably not that simple, as they're not complete idiots. All you have to do is make a clause in the contract saying they can pull out of the deal in case of a major injury that will keep the player sidelined for X amount of months. Another way of putting it is: it's easy to stipulate in the contract that the "injury risk" remains at Juve.
If they do agree to pay 100 mill and take on board the injury risk themselves, they are complete jackasses. I'm not ruling it out, I'm just saying I'd be very surprised if Barca's legal team were to pursue such a strategy.
But maybe

can distract them so they forget to bring up the issue entirely