What is the legal ruling on dismissal from work without investigation, trial, or notification of reasons, especially if issued by a ruler who claims to implement Islamic Sharia?

If the work is governmental, then officials must choose the most competent and righteous, otherwise they would be betraying their subjects and deserving of the Prophet's (peace be upon him) warning of being deprived of Paradise. However, if the work is private, then dismissal from it depends on the terms of the contract and the circumstances of the dismissal. If the lease (employment contract) is for a specified period, then both parties are obligated to fulfill it, unless there is a legitimate excuse that permits annulment.