"If you want my arse, Potter, you'll have to stick your fingers in it first. Now, carry on."

LOL.

What would have happened if both were tops and both refused to bottom?

Oh the complexities of being both bottoms. :-D

Say this story reminds me of another one where Harry and Draco are both bottoms and they solved the problem with a double-dildo. PWP indeedy. :-P