Can Huskar kill Roshan in one Hit?
For the purpose of this hypothesis, Roshan's actual HP does not matter.
Huskar's Life Break upgraded with Aghanim's Scepter deals 65% of a target current HP as damage. Let's represent Roshan's Health as H and Life Break Damage as D.
D = 0.65H*(1-0.55) = 0.2925H
Our goal is to perform a combination of abilities and item debuffs to get D = 1.32H.
Why 1.32H?
because with the equation 100 = 0.65H * 1.16(1.16 is Huskar's maximum spell damage amplification) H = 1.32 Using Items alone, Huskar can carry five aether lens in addition to his aghanim's scepter. In addition to a spell damage boost based on his Intelligence.
D = 0.65H(1+0.463+0.25)(1-0.55) = 0.501H
If you replace one aether lens with a veil
D = 0.65H(1+0.463+0.20+.00625)(1-0.55)*(1+.25) = 0.61H
The max damage a Huskar can do alone is still below half of Roshan's health, but with friends this can greatly increase.
The first assistant will be Alchemist to free up an item slot for Huskar
A Huskar with six aether lens, an Aghanim Scepter Buff, coupled with a veil debuffed roshan thanks to Alchemist brings the damage to
D = 0.65H(1+0.463+0.3+.00625)(1-0.55)*(1+.25) = 0.65H
We're getting closer, now to bring out the heavy hitters
Pugna will be useful for his painless decrepify and the fact that he can easily pop roshan's spell block
D = 0.65H(1+0.463+0.3+.00625)(1+.25)(1+.6)(1-0.55) = 1.03H
Very Close, but remember, we must multiply H by 1.32 in order to kill Roshan. Let's add one more assistant, Ancient Apparition and his Ice Vortex
D = 0.65H(1+0.463+0.3+.00625)(1+.25)(1+.6)(1-0.55)*(1+.3) = 1.34H
We have finally crossed the threshold, it is indeed possible to defeat roshan in one life break with this lineup. If Roshan's magic resistance was even one percent higher, this wouldn't work.
TL;DR
youtube.com/watch?v=ME9Ao5kCTW0
Now you only need to farm 13800 gold and 24 levels as a hero with no aoe skill.