You could hook up an external KB and use it, provided the system still works the way it should be. The old KB is probably shorting at a lot of keys, rendering the system unusable. That is, if the mobo underneath is still OK.
i would remove all power from the laptop (including the battery), and start disassembling it to remove the KB and inspect the other elements underneath. Problem is, you might or might not have access to the CMOS battery and that could prevent some clean-up efforts.
In short, you have a few options:
1. If the system still works, remove the old KB and use an external one. Later you could replace the integrated KB if you still desire. By that time, though, the rest of the laptop might start to smell of rotten soup.
2. If it doesn't work (or if it does, but you feel adventurous), you could disassemble the laptop and clean the parts to your best effort. Ensure you thoroughly dry each part before reassembly. The old KB might still need replacing.
3. Just forget about it and get yourself a new laptop.