I don't think they stop working if they are activated and state program is installed if applicable. If you try to reinstall and reactivate those versions on a new computer that won't work beyond the current year and 3 prior versions.
If they're working I wouldn't uninstall them unless really want to clean up and confident you don't need to access to your old return any more. If you do decide to uninstall make sure you have PDF copy of your return with all forms and worksheets.
