United posted this in another thread but this fits here too.
If you don't resign Butler who takes his defensive zone starts? Do you really want to put Russell, Wideman, or Wotherspoon in that situation or would you rather continue to feed them better offensive minutes.
Or how about his team leading 2:45 SH TOI per game? Who do you want to give that SH time to on our roster?
If you think there is an upgrade available via trade or UFA then you make that deal, but you don't open up his spot to a rookie with nobody else on the roster ready to take his defensive minutes.