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.
I'll tell you two words: Champions League. That is by far the most important club competition in the world, every player dreams to play in the Champions League, many of us grew us listening to the Champions League anthem, and it's more fascinating than any national competition. So the simple fact that Turkish, Portuguese, Dutch teams, etc. take part to the Champions League is a huge incentive for many players. I have nothing against players who chose to play in Saudi Arabia, at the end of the day they pay you 10 more, if you are a mediocre player or old, it's a great option to make a ton of extra money in a very short time.
Also let's not forget that for many European players is difficult to adapt to the lifestyle, that's why many of them want to leave after 1 year. Money is important but there are other things in life, especially if we're talking about players with family, kids.