The possibility of Zaniolo leaving As Roma is quite small, because Roma's relationship and situation makes him comfortable. But if Mourinho had another player they wanted to replace Zaniolo, Roma might let him go. But I haven't heard about it now, about there will be a replacement for Zaniolo next season. So I'm still pretty sure he's still going to stay.
Yep, his current situation in AS Roma makes him comfortable, never heard bad rumors. That player never stated to plan moving to another club in the near future, so it is a strong sign that he feels happy at AS Roma. So far, there is no issue that Mourinho wants to sign a player that has the same position as Zaniolo. Mourinho seems satisfied with him, he must play regularly and be a key player in the lineups if he didn't get injured. Based on this fact, he has no reason to leave.