If they have managed to solve the double spending problem without any need of decentralized participants/players (e.g. miners) then Bitcoin would become instantly useless.
That was never a problem: with a trusted centrally managed server network, is trivial to avoid double-spends, it is basic database application.
The problem that was open for 10-20 years, and that Satoshi hoped to solve with the bitcoin protocol, was avoiding double-spends without a trusted centrally managed network. That is why bitcoin has miners, proof-of-work, and mining rewards.