Sometimes they die for reasons unknown. Even the healthiest of frogs can sometime perish for no apparent reason.

Was their any odd behavior?
Was there anything that could have caused him stress?
What was the last thing he ate?
What makes you believe he had a prolapsed intestine?

More information is needed, but we may not be able to identify cause of death. You may have to seek out a Herp Vet and have a Nechropsy performed to identify exact cause of death. I'm sorry for your loss