In principle, since both the Signal client and server are FLOSS, it should be possible to resist a block in some ways that might not be so easy with for example Whatsapp, but as far as I can tell, as things stand right now there is no built-in way to switch server, and asking millions of regular people to make changes to the source code of their cellphone software, recompile and manually reinstall does not seem like a recipe for success.
I wonder if one might sensibly work around these things by fallback/optional connection to the server through Tor if Tor is available on the device?
No it doesn't. If you're going to wave this flag, you should be complaining about the management controller inside of your CPU (presuming you are already running an open source OS).
>you should be complaining about the management controller inside of your CPU
And I am! I can't wait for Novena! Also notice a difference. Having a close-sourced CPU is different than having a close-source browser which has much more possibilities to compromise you. It can start camera, microphone, read disk files, locate you and transmit everything to "cloud".
Can Signal be taken down like WhatsApp if the same happens again in the future?