Melo played at an elite level at the 4 position offensively last year because he's quicker than most power forwards and increased his efficiency. Defensively, you can cross-match and Chandler can guards the other team's traditional big because every team not named the Lakers has 1 or none of those guys.
Offensively I think the Knicks can make up Amar'e's 15-18 points running pick and rolls to chandler, A jump-shooter like Thomas or Novak and with Melo picking up some of the scoring load.
The Knicks are going to have to be on point defensively to be successful without Amar'e in the lineup but I'm not convinced it's hopeless. I like one of these...
Felton
Brewer
Novak
Melo
Chandler
OR
Felton
Brewer
Melo
Thomas
Chandler
I'd rather keep Smith on the bench and have Brewer play the 2 for Brewer's defense in the starting lineup and Smith on the bench for scoring.