Ronaldo is a key player for Al Nassr, yes of course Al Nassr still dependent him besides being the strongest in team he is also a good striker. But actually there is still Talisca in that team, somehow he couldn't score in match against Zamalek.
Indeed Mane should be able to strengthen game if he can give many assists to Ronaldo, but this is still new for Sadio Mane, after all he still doesn't have chemistry with Ronaldo. I mean Mane has never played in a team with Ronaldo, if I'm not mistaken.
Cristiano is already an old player but he still has very strong body and is very skillful so if his team mates can support him, the coach uses him appropriately, Cristiano will be able to score goals for Al Nassr. It's certainly that he is no longer a player who can score goals in all matches and won't be able to bring Al Nassr to winnings by his goals in most of matches.
If it is simply about contribution for the club, he is useful for Al Nassr.
Sadio Mane at Liverpool was crazy because many praised him when he moved to Bayern Munich he failed in his first season and no season was maintained by Bayern Munich so he was sold at a fairly high value.
Liverpool is a club that brought Sadio Mane to a new level and he got biggest achievements in his club career with Liverpool. Since his departure from Liverpool to Bayern Munich and now left Europe to join Al Nassr in Saudi Professional League, it is impossible for Mane to return to Europe and achieve bigger success in future.
Now that Sadio Mane is at Al Nassr many think he will score goals but it's not a sure thing or a top scorer because the competition in the Saudi Professional League is now getting tougher with Benzema also in this league, but I would like to see the competition become even more competitive, but at least a duet between Ronaldo and Sadio Mane would be more impressive.
He will be able to score goals for them but I believe Al Nassr expect more tactical contributions, key passes from Sadio Mane than goals from him. They already have Talisca and Cristiano who are goal machines for them in the last two seasons.