Rafinha has a good role to play in a 3-4-3. However, if we go back to 4-3-3 it wouldn't be the end of the world if we sold him.
You are right.
We don't know what is the board planning longterm.
If we buy Bellerin and go back to 433, we will surely play:
Iniesta-Rakitic-Busi again.
Gomes will probably stay at least one more season.
Denis also.
Roberto will be a Cm too.
Alena is knocking at our doors.
We might buy someone like Verratti.
Arda might be loaned or sold.
So, if we'll go back to 433, we will have too many midfielders surely in the next season.
On the other hand, I would keep him rather than Gomes, Denis and Arda.
Rafinha was awesome in 343 later and turned to be a much better fit than midfielders bought in the last 2 years.
Don't think that there is a club that would pay 35M for Rafinha. If one pays 25M we should be happy and take the money. If it's less, forget it.
I also think that no one would pay even 20M for him.
He doesn't have any real strengths.
He is good in everything, but not world class in any aspect.
Plus, he could end as one of those guys who is very good in one club but meh in all other clubs.
So, imo, we could sell him only in some 10-15M deal.
Further, if Rafinha is considering leaving then stories about Thiago returning here are just a lie.
If there is a chance that Thiago will return, Rafinha would be happy and he surely wouldn't consider leaving.
Rafinha would surely "know" some inside infos from his brother and there is no way that he would consider leaving if there was even the tiniest chance for Thiago to return.
If Rafinha wants to leave, I don't see which club would pay more than 15M for him.
He is not a player for other big teams (Real, Bayern etc).
About smaller teams, I don't think that they have money for him (except some midtable EPL team), plus again, Rafinha don't have any "obvious" strengths and I don't see why a midtable team would splash a fortune on him.