This makes some sense. It would definitely kill people. However, the hurricane-force winds part is probably not realistic. A meteor impact that melts half the Earth won't just make air get flung into space: the air will become no longer exist as it dissociates into its constituent atoms, which probably means no vacuum. You can't just "fling" air. The rain part doesn't make sense to me, as it's likely that the ratio of water/air is the same (remember, the water vapor on the impact side was dissociated into O2 and H2). Additionally, an impact large enough to turn half the planet to lava would almost surely destroy the whole Earth. 513
The meteor would likely have mostly kinetic energy, and for enough kinetic energy to turn into thermal energy to actually melt half the Earth, the meteor would have to disobey the laws of physics (as a meteor with enough KE to do that would just shatter the Earth and fling the pieces a couple billion miles through the galaxy, instantly destroying the whole thing, and in that case likely won't melt half the Earth, since the Earth won't be able to stop it and turn enough of its KE into heat [Kinetic energy - heat occurs when something bumps into something else and slows down/stops via friction of the normal forces; such a massive/fast meteor wouldn't stop]). If half the Earth actually DID turn into lava, and half the atmosphere id disappear, the planet would become uninhabitable as not enough atmosphere and oxygen would remain to support life (the atmosphere shields us from the hazards of space). In addition, the Earth would probably collapse if half of it turned into a liquid (and likely settled into the core), as a hemisphere is not a viable planet shape. Finally, your "impending doom" is going to happen another way: even if the meteor wasn't big/fast enough to melt half the Earth, the shockwave from the impact would race around the Earth, killing everyone it hits as dust from the blast is flung into the air, obscuring the sun. This even happens FAAAAR before half the Earth melts from an impact (which would shatter the Earth anyway). I'd say that people would have time to leave Earth before the shockwave flattens them. A meteor that would do this would probably be about small continent size (Europe).
(also pretty sure Richter 15 means the Earth explodes)
P.S. if only a little bit of the Earth around the impact melts, lava falling from the sky seems possible and would be cool. 208