If you can turn off servers you run and people cannot submit new transactions on the chain using those servers, then your chain is not decentralized. This isn’t a hard concept.

But, it doesn’t matter that your chain isn’t decentralized for most use cases as long as you can guarantee most of the benefits of decentralization as a rollup with an existing proof system.

Just admit your chain isn’t decentralized and then explain why it doesn’t need to be to give users the protections that web2 can’t provide.