If the core bitcoin team tells miners their mining is going to be ignored if it isn't part of a specific fork because of some credible reason, the miners will follow, no matter how many of them there are.
As I understand it, the core bitcoin team (as well as all bitcoin users) can do absolutely nothing if the majority of the miners ignore their request, as long as THEY agree on a fork to work on.
that's not how bitcoin works. the blockchain (the ledger) can fork into competing chains. if your client and my client disagree about which is the live chain we can't transact. the core bitcoin team can only suggest which chain to consider the live chain. anyone who disagrees is free to use different chains.
