Dammit, bd... now I wanna see that whatever-the-fukkit-is you're talking about!
As a service tech in 4 major disciplines over the last 4 decades, most overlapping, my experience tells me a few things looking at this laptop.
1) Someone isn't being honest here; not sure if it was OP or his friend. That coffee didn't get spilled under the laptop, next to the laptop, or near the laptop. It got spilled IN the laptop. I can tell just by looking at where it pooled that it ran down through the keyboard. How? Hundreds of such repairs, that's how.
2) Whomever it happened to probably tried to just dab it dry and hope for the best. Maybe put it on a towel and let it sit overnight. Then when it worked the next day, thought "No need to tear it down." WRONG. That kind of liquid ingress, unless it's a ToughBook, you ALWAYS need to tear it down and clean it. IMMEDIATELY. If you get in it right away before the liquid dries, you can often clean everything with just a quick rinse of distilled water after disconnecting the battery/power. MUCH LESS assache, much higher success rate.
3) Battery was probably drained by liquid shorting active components to the point the BMS in the pack went into shut-down. IF YOU'RE LUCKY you might be able to disconnect from mainboard and recharge the cells directly using a LiPo charger set to very low current to "wake it up". More likely will need replacement battery.
cdev hit the nail on the head; disassemble down to the bare board, scrub with soft toothbrush using distilled water then alcohol, then dry mainboard on a towel for a day or two under a incandescent lamp, or on a hot dashboard of a vehicle in the sun... or in a food dehydrator if you have one.
While that's happening, clean out the chassis using the same brush & solvents. Clean carefully, use towels/dishcloths to dry, and Q-tips to get into all the nooks & crannies. If there are daughterboards at power/USB/Thunderbolt ports, remove and inspect as well. Clean as needed, reassemble.
Putter around with battery while things dry. If you get lucky and you charge the cells and you get voltage at the battery connector, yay! Usually you'll have to plug it in and plug in the AC adapter to get it to turn on though. Whether to spend money on a new battery is up to you; if it's a couple years old, you should probably consider it "PM" and get one coming anyways. Your keyboard is probably gummed up all to hell from the coffee; get one of them coming too unless you're absolutely positive every key works, doesn't hang and is never "intermittent".
Reverse disassembly to reassemble. Don't cheap out on reassembly; if you have damaged silicone thermal pads from disassembly, source new ones. Clean/replace thermal grease as needed. Make sure the cooling fan/fins are clean, and that the fan turns free.
Cheers, and good hunting;
mnem
I would totally pay to see that.