Call failed

I wanted to test my daughters new apple

watch with cellular after after we unpaired her old one. The main reason we have cellular for her watch is safety and security as she’s a runner and doesn’t run with her phone. She’s also off to college this fall so it’s just an added security measure. 

So to make sure it was working properly since her phone was sitting right beside me - I decided to turn it off to make sure it rang on her watch so it wasn’t potentially picking it up via WiFi or bluetooth. To my surprise It didn’t even ring and gave me called failed. 

I duplicated this on my wife’s phone and watch as well. 

So not only do calls not go through to  cellular watches when the paired phone is turned off  - they’re are not even being sent to a voicemail. 

First attempt was calling form my iPhone 8 to an iPhone 11 paired to an aplle

watch 6 from my iPhone 8

Second attempt to my wife’s iPhone 8 paired to an Apple Watch 3 from my iPhone 8

third attempt called to my wife’s pairing from my daughters iPhone 11 

All devices updated to latest iOS all

had same outcomes - call failed on outgoing call device 

So if someone’s phone would be dead their calls would not be forwarded to a paired Apple Watch or to their voicemail?