There is Always Consensus.

At any given time, every single player in a crypto coin network is inherently 100% committed. You can either work with the network as it is, or not participate. This is always the option. There are multiple compatible versions sure, but ultimately you're fully in, or fully out. Play by the system’s rules, or don’t play.

The recent Bitcoin Cash hard fork illustrates this perfectly. Leading up to their split from the majority, they needed to be running a fully compatible version of bitcoin that works with everyone else’s software. So it wasn’t a matter of all the Cash miners simply agreeing to load up some new software at 5:20am Aug 1st. What they did was write a version of bitcoin software that was fully compatible, but had a scheduled change in its parameters at 5:20am Aug 1st. At that time everyone running the Cash version would become incompatible with the rest of the network and split off as their own network.

This happens literally from one block to the next. When Bitcoin hit its 478 558th block, everyone was fully committed to it, 100%. However at block 478 559, the Cash miners changed to new rules and were no longer recognized by the rest of the network. Completely and fully separated with no connection between them.