Coffee spill on MacBook Pro Retina
In situation as you described, HDD could survive with high probability, but as MBP retina uses SSD instead there is a small, but chance to kill it. First steps to repair it is to disconnect the battery and disconnect the SSD. This is guarantee to prevent:
1) future information losses
2) future damage of logic board.  

What damages can you expect - generally, in these cases this is 50/50 game. Cleaning requires disassembly of the MacBook and wiping board with cleaning agent e.g. ethyl alcohol (96% concentrated). It is non-conductor, so then when macbook will be reassembled, it probably will work.
My friend had similar problem: water and MBP retina 13. And now his MBPr works OK, but only with power cord plugged in. I do not recommend connect it to power cord until it properly dried and cleaned (with alcohol).