Blazing Constription says "Until the end of the turn" whereas coward reads "At the end of your turn".
They both proc at the same time, so its up to the current player (the one controlling the Phoenix Elves) to decide the order these abilities will proc.
Can the current player chooses to end his control prior to rolling the dice (i know he probably wont want that, but who knows)?
This. The PE player might not roll if he wants to kill it as magic or BC it again the following turn. Keep in mind that Kreep would have to be adjacent to an "enemy" unit: in this case one of the Sand Goblins on the other side. Maybe he'd run from that scary dude Biter!