One of the things you can do with SQL Server Agent is to automatically restart itself, or even SQL Server, in the event that the service unexpectedly stops. Just right-click on the SQL Agent service inside of SQL Server Management Server (SSMS):
If the SQL Agent service should stop unexpectedly it will now attempt to restart itself automatically. This is the preferred setting if you are relying on scheduled jobs you are expecting to run correctly. You can get more information here.