The most senior devs already left the sinking core ship. More will follow.
The question is really not how many will leave. Its how many will stay and fight, and how much damage will they do.
What damage can <25% of hashrate do?
At this level my guess is that would just decrease the rhythm of diff increase for a few days or weeks, and later on everthing would go back to normal again.
i'd agree, and given the 750 mined blocks courtesy period extended to those who haven't upgraded I think it would be in the best interest of any stubborn minority to accept the consensus view