In a web browser, YES
You do need a live connection to view the data in a web browser.
In Google Earth on the desktop, NO
Since we have provided the route data as a KMZ file, you can open and view these in the desktop application Google Earth at anytime and do NOT need a live connection to view the data in the desktop application.
Google Earth requires a live connection to download the Google location data (roads, places, landmarks) and background data (street maps, satellite images). These points of reference will be missing UNLESS you pre-load this information into your cache first. Say you want to show the route data on a laptop but you will not have an internet connection - like at a public meeting or a motorcycle race.
Open the KMZ files with a live Internet connection. Pan and zoom in on all the areas of interest. The imagery you are viewing is being stored in a folder on your machine - a 'cache folder.' As you move arpund in Google Earth, the application first looks in this cache folder to see if images it needs are already there. If they are, those images are used and it saves waiting for them to download again. If not, it will go to the Internet and retrieve the needed image(s).
If you will be relying on cached data, check out this link to maximize the amount of data you cache.
Memory and Disk Cache Preferences