There is no trigger involved when he casts a creature spell. The effect of Soul Sculptor just ends. You do not gain a life for that because nothing enters the battlefield at that time. From the glossary of the rules:
Enters the Battlefield
A nontoken permanent “enters the battlefield” when it’s moved onto the battlefield from another zone. A token “enters the battlefield” when it’s created. See rules 403.3, 603.6a, 603.6d, and 614.12.
It didn't "return" from anywhere. Has it been under that player's control since the start of their turn? Soul Sculptor doesn't alter that. The "summoning sickness" rule doesn't care how much time it has spent as a creature, just how long it has been under their control.
302.6. A creature’s activated ability with the tap symbol or the untap symbol in its activation cost can’t be activated unless the creature has been under its controller’s control continuously since his or her most recent turn began. A creature can’t attack unless it has been under its controller’s control continuously since his or her most recent turn began. This rule is informally called the “summoning sickness” rule.
The duration is "until a player casts a creature spell", not "until a player casts a creature spell while Soul Sculptor is on the battlefield". The enchantment effect ends. Just like the effect of Giant Growth ends on schedule even if Giant Growth isn't on the battlefield at that time.
611.2a A continuous effect generated by the resolution of a spell or ability lasts as long as stated by the spell or ability creating it (such as “until end of turn”). If no duration is stated, it lasts until the end of the game.