Question

Hot dogs and hot dog buns are complements. if the price of a hot dog falls, then

Answer 1

Then the price of hot dog buns would go up, I assume.
If you were the owner of the leading hot dog bun company, and hot dog prices went down, then more people would need to buy hot dog buns. So if you wanted to profit from that you'd raise your prices a little bit to make more money.

Answer 2

Then a lot more people should buy more hot dogs