Meshtastic is an off-grid wireless mesh communications network so it doesn’t rely on Internet or cellular connectivity. It is primarily used for text based messaging at the moment but people are looking at how Bitcoin transactions can be transmitted over it so it could be used as you suggest for sending transactions where there is no Internet or in situations where the Internet is down.

It is very slow compared to the Internet and other forms of networking so I don’t know that it could ever make up a large portion of the Bitcoin network but there are definitely possibilities to use it in some way.