Oh no!!!
Was doing some maintenance on my system, and noticed that GOOGLE has done away with the api support required for this plugin.
They have switched to a WWGA (works with google assistant) api, which is currently not available until late 2020???
The existing api still appears to work, but unfortunately for me, I merged my account as suggested and that has effectively killed my ability to use the NEST home plugin.
I'm sure the developer is aware, but just a note to all who use it to beware and don't make any major changes:(