I just came by Realmwright and it didn't give any discussion on whether the changed lands are permanently changed or not if the creature leaves the battlefield.
Does anyone have any info on this?
The short answer is no, they'll lose whatever type they're given when Realmwright leaves the battlefield. The reason is that Realmwright has a static ability that creates a continuous effect that dictates that the lands are of the given type:
Since Realmwright's ability is the source of the continuous effect giving the lands the specified type, the effect will end as soon as Realmwright leaves the battlefield.