The beauty of external Google calendars is that you don’t really download them — just a link to a calendar so if the linked location changes your calendar does to (so new dates, times, events get passed along). I have a number of external calendars that I use(and have created a few – including a very detailed minute by minute one for UCR DE weekends).
I am not sure if the calendar that comes out of the WordPress link will update if you change things in the calendar that you have created.