As far as I know, compensation from FIFA is more of a formality than a really significant amount.
As for Al-Hilal, on the one hand, they have reason to consider themselves deceived, but on the other hand, this is the well-known (in a bad sense) Neymar, the risks were known and understood in advance. It seems to me that many wrote here that this is a strange transfer, and given Neymar’s salary, it is unprofitable. But Al-Hilal decided to take risks and they were unfortunate in that these risks were realized.
Neymar didn't really create much impact on the pitch for Al-Hilal before he got injured he's not a player they could really depend on to win a match, they still got other good national team players that could replace Neymar till they sign a new replacement and also there striker Mitrovic is still very fit and active currently, however they're be on a great lose paying him a hefty wage bill while he's away from the squad.