Testing Microsoft Teams Phone System

We're testing Microsoft Teams phone system with a very select few users.  One of our major concerns moving completely to VOIP/SIP is access to emergency services with an Internet/Power Outage.  Our current infrastructure is grounded in POTS lines using FXO ports with an in house PBX (UC560).  

Our company (a preschool) requires the highest level of access to emergency services.  How are companies leveraging Microsoft Teams telephone service with guaranteed emergency services?  Only POTS lines provide dial tone with power outages and internet outages.