We have seen some players who went to Saudi league and then made a comeback too, so that is already proven to be possible for many players, and if he wants to, he can play for 1-2 seasons and make all the money in the world and come back and play wherever he wants.
Saudi Pro League attract players by giving them a good incentive, money, but let's be honest to say that the quality of the league is better than many European leagues. I don't think that Turkish league, Liga Portugal or Eredivisie or even French Ligue 1 are superior than Saudi Pro League honestly.
So a player who wants to move to Saudi Arabia will benefit from excessive money and a good competition, let's say respectable level. Maybe the main things missing are the entertainment and the climate that European countries have and are different in the kingdom.
The possibility to regain a good place once a player pass a season or two in Saudi Pro League is always possible. It depends from the quality the player showing in that league in fact.