The answer is NO, and YES.  No, you will not lose any data (maps, markers, etc.) that has been stored inside the tables.  However, you will lose the following when you reinstall or upgrade:

1. Configurations - configuration settings in either the mambot/plugin or the component will be lost and will have to be re-entered
2. Icons - This does not include the icon definitions in your tables.  This does include all of the icons that have been loaded into the GMaps icon folder.  This folder does get removed when performing an uninstall using the Joomla installer.  You will want to backup your icons folder before uninstalling the component.  Uninstalling will the mambot/plugin will have no effect on the icon folder.