After an expert gets to the Space-Time Realm, they arguably become immortals. They won't die unless some external factor kills them directly. Lifespan ceases to be an issue.
However, that didn't mean nothing changed forever, especially after an expert reaches the Celestial Realm. From the moment you reach the Space-Time Realm, you are destined to 'lose your heart' one day.
To be honest, that's just a nice way of saying that you will eventually go crazy. In some cases, those experts went into a complete rampage, killing and destroying everything they could find.
Space-Time Realm and Divinity Realm weren't as bad, though. This 'loss of heart' happens many times slower for them, and you would be hard pressed to find any information of a single expert at those levels who lost their heart. It was much easier for them to die way earlier than that for other reasons.
