In the manga, the duration of Gojo's seal is not clearly defined. It's left somewhat open-ended, allowing readers to interpret it based on the context and events that follow.
Perhaps Percy discovers a secret that is so dangerous that the powers - that - be decide to seal him away to keep it safe. It could involve a prophecy that he might fulfill in a way that would change the world in a way they don't want. So, they use some ancient magic or a powerful artifact to seal him. For example, if there's a prophecy about Percy uniting two warring factions in a way that would upset the current balance of power, those in power might try to stop it by sealing him away.
Sakura might be initially shocked and worried. She'd be concerned about how this new entity within Naruto could affect his health and stability. But she'd also be curious to see if this could give them an edge in future battles.