Counterfactual hypothetical:
Villa plays Saturday, but just about everything else goes exactly was it was, or as near as can be. Bottom line: it's minute 84, we're winning 4-0, and Harrison earns a PK. Villa is scoreless and Lampard is sitting on his brace. Who takes the penalty kick? Does your answer change if Villa has one goal, presumably the Taylor one? My guess is Villa let's Frank take it regardless, but my confidence in that is only moderate.
Frank takes it 10 out of 10 times. If you are up 4 goals that late (the game is essentially over) and a player is sitting on 2 goals, you give it to that player to get his hat trick. Now if Villa and Frank are both with 2 goals at that moment...then it gets complicated. Most likely Villa takes it then as he's the leading scorer.