(All info below is as far as I know, correct me if I’m wrong)
Yes, it should work fine during a ISP breakdown, except for my.homey.app (Advanced Flow 
), while that site doesn’t run @ Homey itself,
and,
after a certain number of weeks without internet (is that a reality @ your place?), monitoring/managing by the mobile app will not be possible anylonger, the cloud is needed to renew authentication
Also, this statement @ homey.app does have the ‘but’:
“The cloud is only used when absolutely necessary”.
.
But, my but is: Athom, shouldn’t the statement below be extended with:
“, but to monitor or manage your Homey, every now and then you’ll need the cloud to authenticate, and to use Advanced Flow, using my.homey.app, you also need the cloud.”?
And
“Of course cloud connected/dependent devices don’t work without the cloud” (this is not obvious to non techies)
You can write to https://homey.app/support
(Isn’t this info available in the documentation which came along with your Homey?)
