How do I completely delete the router and anything remembered about its interfaces so that I can add it back and see all the interfaces again? Or is there another way to get all the interfaces back again?

The two choices with device interfaces on maps are delete and hide. When you select the interface on a map and delete it, as you said, it will re-appear after a reprobe has been done. This assumes that the box in the Interfaces window marked “Allow Periodic Reprobe” is selected – your description seems to indicate it isn’t. If this box is cleared, periodic reprobes will happen twice a day. Also, you can right-click the device and use “Reprobe selection” to do a demand poll (assuming you’re monitoring with an SNMP probe so you get interface data).

Selecting the “Display unnumbered interfaces” box in Interfaces is an option primarily for switches or hybrid devices with interfaces which don’t have assigned IP  addresses. By default, if you add a device to a map and monitor it using SNMP, the interfaces which show up are the ones with assigned IPs, and they connect to subnet ovals on the map. Un-checking them in the Interfaces tool is “hiding” them. It shouldn’t make InterMapper “forget” them. They should remain in the listing, with their checkboxes cleared.

Re-adding devices to the map is likely, although not guaranteed, to cause a device to use the same device ID it had previously, and for residual map information to be applied to it. We have no mechanism in place to wipe devices as opposed to deleting them. If you can’t get an interface back use SNMPWalk to walk the ifTable and verify that the monitored device still shows the interface (covers the case where an interface module was yanked out of the chassis).