@Nossio 

Hi, welcome to the community.

Can I have more details about the issue here "When my internet connection fails my entire network is gone"?

Would you please share a picture/diagram of your network topology?

When internet service is off, the mobile devices on Deco are still able to communicate with each other. 

" Archer AX73 but this one isn't compatible with the Deco mesh system", I think you might refer to OneMesh/Easymesh isn't compatible with Deco Mesh since Archer AX73 does work with Deco but their Wireless networks would be two seperated Mesh networks.

Thank you very much and best regards.