Waves is very much decentralized. The only centralized element of the Waves Platform currently is the Gateway provider, who are a UK registered company, so very unlikely that would get shut down anytime soon, if ever! This is also only temporary as WavesGo and a number of other projects have been working on Gateways or Blockswaps to facilitate on-boarding more Altcoins. The Gateway provider is key for easily on-boarding FIAT but with Waves working so closely with Govenment, Deloitte and Tokenomica they will always find a solution for on-boarding FIAT.
Other then that, anybody can run a Waves node and Matcher keeping the blockchain and DEX alive.
Hope this helps.
RE: How the Waves Platform are Building the Foundation to take Blockchain Mainstream