Hi Jose,
Unfortunately I dont think we have a trigger to do that as far as I know. My first thought would be a data partition constraint, but that wouldnt work because it would have to calculate the time between date closed and current date/time which there is no function to do within data partitions. You probably could do this with custom spelcode, but I am not sure what that would be as its outside the scope of support so we dont have much experience with that. One last thought that comes to mind thinking outside the box, (and i am honestly not sure if this would work at all but might be worth a try) is to have an event that is invoked when a ticket is closed which has a delay time of 7 days, which would then have an action macro that sets the status to a new status you create, called "Final-Close" which would also set the ticket to inactive just as the closed status does, but then you could do a status transition such that you cannot go from "Final Close" status to any other status. That may work for you but i cannot say for sure - you would have to test that all out in a test system.
Hope this helps a bit.
Jon I.