The interface would become archived if Iris no longer receives data or if there is missed data from the link. As long as Iris is still able to ping the link, it will just report as down.
The best method when you are closing/deleting links from a router would be to delete the corresponding mnemonic in Iris. This will cause Iris to stop monitoring the link and no alarms will be generated for it.
To do this, click the dustbin icon next to the mnemonic it will remove it from Iris and the graphs will go into no data status and will be archived over time.