When you click the settings button in Monitoring and select the Thresholds option you'll find all the available monitoring graphs. Including IOPS, listed under the Disk header.
I am not completely sure. On my test server historic data was saved (ie not deleted) and still accessible after re-installation of the extensions. But can't grantee anything.
I have tried to remove and reinstall the Monitoring extension a couple of times (the historic data is kept) but I don't get the disk IOPS graphs. Is there a way to add them manually?