it's not just the coaches though, but also the players. take for example steve francis and cuttino mobley, they were unseparable in houston and the trade that sent them to orlando. but regardless with their friendship, mobley was being shifted to sacramento in xchange for defense support, doug cristie.
such as the other players, whom a team tends to inexplicably talk about the business that they are being already traded to the other team. there are so many cases like this in the NBA, but again, it's sports business. no matter how deep ur relationship it is with ur team or with a teammate, it's impossible to be on that team for too long - not if ur a franchise player, ie the reggie millers and the john stocktons in the league.