My idea is so obvious I'm surprised no one has thought of it. It's definitely a must-have, I think.
I suggest that when the grid comes back online or when a region restarts that there be an event handler to be triggered.
That way if downtime effects the smooth running of your script you can use this handler to tidy up any problems caused by the downtime.
For example I was creating a script that uses llSetTimerEvent to to trigger the timer event every 24 hours at midnight. When the grid goes down, for example for the 5 hour maintenance, the timer event will be delayed and be triggered 5 hours late. Currently I have to regularly check to make sure it is still scheduled to trigger on time, for example every hour. But if your script is very time sensitive you would have to make the checks very short such as every minute which would affect performance, especially if you have many objects with this script in them.
With my suggested event handler you would set the timer to trigger every 24 hours at the correct time then use the event handler to correct the timer when the grid or region comes back up.