"Pour" is optional in this case, as far as I understand it. For the sake of translation, "le voir" is already equivalent to "to see it", but you could add "pour". "Il vient nous sauver" = "il vient pour nous sauver". There may be a slight difference in nuance, but it's essentially the same.
Retourner is one of a group of verbs (movement like aller venir monter descendre, volition like aimer vouloir pouvoir devoir etc) that takes an infinitive without preposition. Tu dois aller le voir. (You must go to see him). Je descend à la cuisine boire un verre d’eau. (I’m going downstairs to the kitchen to drink a glass of water.)
Not sure where to find a relevant lesson here, maybe someone can point it out?
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