Copy of spell triggered by Flamehold Grappler did not go on the stack:

• Played Flamehold Grappler (trigger for copy next spell)
• Cast Rebellious Strike targetting another creature
• Rebellious Strike goes on the stack, this should trigger Flamehold Grappler copy
• Opponent removes target for original Rebellious Strike (copy did not go on the stack yet)
• Original Rebellious Strike fizzles (normal)
• Copy of Rebellious Strike never went on the stack, was never able to select target, did not get to draw card, lost game.