I think Saudi Arabia will qualify for World Cup using any possible way.
Football have gone passed that stage where a single country can influence the outcome of a particular game..in the case of Saudi Arabia qualifying for the world cup is possible. It also depends on the opponent they meet or play against. If it's a stronger opponents,then the chances or the probability of them qualifying will be slim.
They spent a lot of money to buy Ronaldo and other European players, they also become the sponsor for Club World Cup, after everything they done for football, would they accept if they're not qualified for World Cup.
Saudi Arabia is a very wealthy country vast in abundances of Rich minerals resources so money isn't a problem for them. Signing Cristiano Ronaldo to play in their domestic leagues and also been a major sponsors of the Club world cup doesn't mean they will still be promoted if they failed to qualify to the next phase of the world cup. FIFA have setup rules in every football competitions and the world cup is not an exception. If Saudi Arabia failed to meetup with the rules of the game,they wouldn't be allowed to progress further.