Draw Fire specifically states that you target "THIS" character, in which case the attacker failed his save so he has to attack C-3PO. In order to attack the character with Stealth the player would already have had to have a legal target before Draw Fire was used.
Here is the sequence-
Player A is the attacker. They choose to attack said character with Stealth. This attack must be legal. C-3PO is in Player B's squad and is within 6 squares of character player A is attacking. Player B responds to the attack with the Draw Fire ability. Player A fails the save. Player A now must target and attack C-3PO. If Player A made the save then they would follow through with attacking the Stealth character.