a. Sad End
After a confrontation with the BO, some member is preparing to kill Conan, when Haibara intercepts. As she dies, she tells Conan stuff ("Tell the kids I moved..", "The antidote is blah blah blah..") BUT she does not tell him she loves him (obvious ShinRan fan here)
I BEG YOU GOSHO DO NOT MAKE THIS ENDING COME TRUE!
b. Happy End
Haibara, free from the terror of the BO, remains the size of an elementary school student since she has no one to return to as Shiho Miyano. She still lives with Hakase, and often advises Shinichi (who has grown back for good!)