I've seen that happen (which brings up the separate question of does it matter if the team is N x more productive because of co-location)

I've also seen them stay.

I've also seen them start out very sceptical and then grow to like it (I was in this category - assuming I'm vaguely competent of course ;-)

I've also seen folk I hugely respect advocate and instigate this sort of environment.

.... so which anecdotes win... dunno... hence call for any folks who have found research on the topic.