"What if 1... Bxf6?"

I think then will be mate in next 4 moves anyway :)

1... Bxf6 2.Qxf6,Qb6+ 3.Kh2 (or Kh1) 4.Qg1+ Kxg1 5. Any Legal Move, Qg7# 

well you're right that it's not necessarily mate in 4 ..

 but after 2. Qxf6 black's fate is sealed.

i think mynameisluke meant this

1... Bxf6 2.Qxf6,Qb6+ 3.Kh2 (or Kh1), Qg1+ 4. Kxg1, Any Legal Move 5. Qg7#