Torba at gab went through these attacks and more, had to build what sounds like his own datacenters with network peering agreements + his own banking system since every other business partner in comms/finance was threatened until they dropped him.

So it can be done, but its hard to the point of being commercially implausible. I guess parler didn't survive, but maybe it was never seriously intended to be 'uncancelable'.

Still waiting on Project Odin by the way...