Not to sound harsh, but when will people learn that backups are extremely important and probably one of the first things they should do with data. I have backups in house, in cloud and off site. I am never nervous about losing my data. Data recovery is a lot more expensive than an initial backup system.
The answer to your question is obvious: Clever people learn from their mistakes. Wise people learn from other peoples mistakes. Stupid people never learn, clever people learn after their first costly data loss, wise people learn when they hear of other people's costly data loss.
The thread also gives a clear example that "a little knowledge is dangerous".
To the original poster:
I'd make an appointment at the Apple Store, and they should be able to restore the OS. If any error messages come up, they should be able to handle that as well - much better than we can when we can't see the exact error messages. It's not really much work for them; you'll just have to stay in the store for quite some time until internet recovery has finished, so don't get an appointment late in the evening. They _may_ have an installer on an external disk, which would make things a lot quicker. Next, buy an external hard drive and turn on Time Machine. Because one day, may be in five years time, your Mac will break beyond repair, and then you'll want a backup. (Also very handy if your MacBook is stolen).
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I think this will happen about the same time that people learn not to place cups full of liquids next to their laptop computers.
My grandchildren learned the hard way that if they hold cans of soft drinks, all laptops and iPads disappear and don't return. (They were also told that unlike their parents' car, granddad's car wouldn't start unless everyone had their seat belts on; by the time they figured out the truth, they were used to wearing seat belts).
