Good. They shouldn’t.
Unencrypted channels are the ones that are easiest to trace, and the easiest ones to successfully base a prosecution on.
The most correct response is to report them to law enforcement. Unencrypted channels make amazingly effective honeypots. It’s fairly easy to bust people using unencrypted channels, esp. because people think they’re anonymous and safe. It’s much, much harder to bust people once they move to .onion sites and the real dark net away from their phone. When you shut down all the easy channels, you push people into areas where it’s much harder, almost impossible, to root them out.
I think that holding the executives and BoD in criminal contempt of court is a good place to start.
EDIT: AFAIK Telegram doesn’t use warrant canaries.