Dear @pete
I was curious too!
I De-actived & Deleted My Lay Theme
and re-installed it from the basic original Folder - Lay.zip,
My content was still there waiting,
Screen Shot 2020-08-26 at 8.03.25 PM.png
Screen Shot 2020-08-26 at 8.03.32 PM.png
Screen Shot 2020-08-26 at 8.03.39 PM.png
"Projects" now being "Posts" -
And then when re-installed My content was still there,
Screen Shot 2020-08-26 at 8.11.45 PM.png
I would always advise backing up the folders through your Webhost as a safety precaution, be careful :)
Hope this helps
Best
Richard