Yes it will definitely be a very long negotiation process about Nunez's future with Liverpool, I mean they will have a more complicated communication if Nunez doesn't want to be in the Arab League. I also think Liverpool are a professional club and they will definitely not force themselves to do it, even though they really want to get profit from the sale.
The player exchange option I think is good, but they will also definitely negotiate about the additional price they want. Because I'm sure they also don't want to just exchange players without any additional cost.
It will be a big lose if he play in Saudi Professional League, he's the best striker in Uruguay, so he should being consistent and try to learn everyday in order to carry his team. If he move to SPL, there's a big chance Uruguay will become a mediocre team.
Al Nassr really looks very enthusiastic to get Nunez, but indeed if the player does not want to be in the SPL with Al Nassr then it will be difficult for Liverpool to convince the player, there are other rumors that AC Milan are interested in bringing Nunez.
I don't know if there is connection in the Uruguayan national team if Nunez goes to the SPL, even though he plays for any team but when Uruguay has match schedule then Nunez can strengthen Uruguay, I actually think the departure of several main players one of whom is Nunez will actually have negative impact on Liverpool.