What would hapen if....?

She'd probably be able to cast another jinx just as well...
(Growing up with 6 brothers and all....)

WWHI Snape didnt favor Draco?

His friendship with Lusius would be no more, I'm sure.

WWHI: Slughorn had not been convinced to work at Hogwarts?

Hmm, well DD wouldve had to find another professor. Plus, he & Harry still wouldve had to seek out Slughorn to get that memory....

WWHI Voldemort hadnt cursed the Defense Against The Dark Arts job?

Probably Quirrell would never got the job with Voldie in the back of his head...

Wwhi: Dippet would have gave Voldemort the job when he first ask for it?

He would've wrecked havoc on Hogwarts & the minds of many students....

WWHI Harry didnt have an invisability cloak?

Oh! I just can't imagine Harry without the invisivility cloagh... How could he spy on Snape and listen to other people conversations and visit Hagrid?

Wwhi: Draco would have killed Dumbledore?

That'd be awful...
But just as long as Harry still took Draco's wand, the outcome at the end could possibly be the same.
But then, that would also likely prevent Snape's death as well, so Snape would've had to relay crucial info to Harry so he could figure things out before facing Voldemort.

WWHI Krum went to Hogwarts instead of Durmstrang?

then i think that hermione and krum would end up together

WWHI:
harry had never gotten the firebolt

He would have been able to buy himself another Nimbus, probably.

WWHI: Harry had decided that he wanted to be Dracos friend instead of Ron?

Bad mistake....He wouldnt have the care & support of the Weasley family,
He wouldnt have had Ron & Hermione to help him out of tight spots- as Draco despises them both, He'd have the loss of such incredible friendship.

Ultimately, a friendship w/ Draco would likely have lead Harry to his doom...

WWHI Dobby never helped Harry?