Why is no alerts when my HA goes of line or the resources are to low, like ram and Disk space, the things a Cloud monitor and access should have. Just an Observation 
Look like duplicate of this
This HA offline is good
The others like (disk space) could be done with automation
I like your suggestion but I recommend local devices monitoring Home Assistant. That’s the best way to know whether it’s just an internet outage or a problem with your HA server. That isn’t to sat Nabu Casa couldn’t have a role.
Like an uptime robot, nabu casa could check if HA si up… But I think too, for other alert it’s HA local role