Yes. The NAV CD can be ejected and the NAV function will still work. The last several destinations are retained in memory.

The NAV keeps a certain amount of area data in memory, so you can even change routes without reinserting the CD as long as it's local to the area already in memory. As long as you don't disconnect your battery leads, it will retain the info.

If the NAV needs more info, it will display a message asking for the CD again. At that point you can give it a quick update (it takes only seconds), and then remove the NAV CD again.