The quit method is used to terminate the application. This will pop-up the usual model save prompts if there are unsaved models open. User can cancel the model save, in which case the application will not terminate.
Also, - if there is an other instance of Sketchup is running it will not terminated.
Perhaps reload the extension will be enough in case there is no changes in the menus…
e.g.: Reloading my plugins - #2 by eneroth3
Otherwise I agree with @TDahl and @tt_su that inform the user to restart will be necessary to use the new version, and let the user decide what to do…