“We’re aware of reports that access to Signal has been blocked in some countries,” Signal says. If you are affected by the blocks, the company recommends turning on its censorship circumvention feature. (NetBlocks reports that this feature lets Signal “remain usable” in Russia.)
I wasn't just talking about blockage but also servers being taken down physically or via ISP. I don't think I'm nearly as well versed in Signal as you are to go into depth of how it circumvents blockage via protocols but I assume they don't decentralize their hosts.