Tell him you will go halfs on a replacement screen from another repair shop that dosnt charge an insane price or tell him to go f*ck himself for being a d*ck.
YOU don't put a computer on a FOOTSTOOL. Foot Stools are for FEET not computers. Sorry I would tell him to take a hike!
IMO it's NOT your fault. He's mad because he did something stupid and would take responsibility for his actions. Do not pay for it, not even for a part of it.
While back someone posted that he left his macbook on the floor and his girlfriend stepped on it, the floor isn't a spot for laptops.
Tell you friend to read this tread.
Accidents happen, if he was a true friend he wouldn't do this to you.
I would pay half, but depending upon the model, you may be able to get another for less than $1300. I mean, if he tries to push you ... see if you can't get it replaced and tell him to give you the old laptop. Bottom line is I can't really speak to who is at fault and such, I would say it was 50/50.