An explanatory expression such like 雪かきをしてくれてありがとうございました sounds quite unnatural in a conversation. As you can see, Mike-san doesn't mention the action 雪かき at all either, since it's obvious what you are talking about from the situation. ありがとうございました should be ありがとうございます, because of the same reason as お疲れさまです.
(In the first place, ありがとうございます is hardly used here because they are not doing it just for you.)