As I found out now, you can get the time the server started with:
FROM sys.dm_os_sys_infowhich happens 13 seconds before the tempdb is created - in my case.
What I decided to do is to check when the job had been executed successfully for the last time; you have to trace the jobs id first.
If this time difference is smaller than the scheduled repetition of the job, any unavailability of data must be related to a failure of the measuring. If the time gap is bigger, then the Server must have had downtime in the meantime.
select DATEDIFF(MINUTE,last_executed_step_date, GETDATE()) from msdb.dbo.sysjobactivity
where job_id ='0A362493-B516-4EC2-8189-983584A96CF5' and DATEDIFF(MINUTE,GETDATE(), next_scheduled_run_date) >0If the server doesn't reboot successfully, ... now this is a good question?! Can I check from other SQL servers which istances are currently running?