I’m not sure if there is a great need for this, however I run two voice assistants on my system - the first utilising online connection to process fast, and a fallback integration that only gets used when internet goes down.
I wanted a way to detect this and reroute requests, so conversation router became a thing.
You set it as your main voice assistant, then define the rules and the conversation agents you want for each ruleset, and as the title suggests, it routes the conversation to whichever agent matches the ruleset.
I only have it set for online/offline routing and have not tested other scenarios, but it may be of use to you.
While its waiting for HACS inclusion, you can manually install from GitHub - oooshk/ha-conversation-router: Routing System for Home Assistants Voice Integration based on a rules template · GitHub