incase the executor expires then the validity of the power of attorney stands cancelled immediately. you need to give fresh power of attorney. but never make it irrevocable as you are taking a big risk. Make it revocable power of attorney and also keep a validity period of the power of attorney.
yes you need to execute a fresh power of attorney as one of the executor has expired. therefore, it has become an invalid power of attorney.
Since, three persons had given power of attorney out of whom one has expired, therefore if the document is produced before the third party, the said party might not be aware of the death of the one executor and could be misused.