I've since given it over 24 hours to dry out, and I've also taken apart the keyboard to wipe it down - there was dried hot chocolate residue in it. I will try turning it on again in a while to see if the keyboard now works (it stopped completely, just made beeping sounds), and have done a search online for spare keyboards
In worst case your motherboard or a RAM module are dead. The beeping sound at the beginning of the booting order appears because an problem on the motherboard was detected.
Several times ago my girlfriend spilled a coke on my keyboard. The notebook didn’t boot up and I thought it’s a serious issue… but I’ve removed one RAM and the notebook booted fine.
However, check your machine again and maybe it will boot up properly.