wow mendel, that looks pretty bad... but you can definitely safe the board. What did the battery read? Did it say NiCD? If so that would indicate that the leakage is not acidic, but basic. So to neutralize the leakage you should not have used bicarbonate sodium which is basic as well, but something acidic like vinegar. (If the battery read something different, research online what kind of leakage you're dealing with.)
The first thing I would do from where you're at is neutralize that bicarbonate stuff (and perhaps the leakage) with vinegar. Then remove the vinegar by rinsing with lots and lots of water (you can put the board in your sink to do this. Tab water is fine most of the time, if you have distilled water is even safer) and dry the board. If you wet other parts of the board, be sure to get the water out/off of there too (especially chips can trap a lot of water under them, use compressed air to blow it out). Hand-dry with a clean and soft cotton cloth. Easiest way to make sure the board is really really dry is heating your oven to ca. 70°C, then turn it off (!) and put the PCB inside over night.
After that the leakage should be gone. But it will have damaged the coating of the PCB, so putting some protective solution on there is a good idea (contact cleaner works if you do not plan to have the board stored in a moist environment).
I hope that helps and you get rid of the leakage. I've seen boards where the battery fluid had crawled between the different layers of the PCB and was continuing to eat it away... but that doesn't seem to be the case with yours. Even in the worst scenarios a thorough cleaning will stop or at least slow the process immensely (so far it will take another 5-10 years before the first traces get harmed), so you should do it in any case. I'd slap a battery holder on there when you're done. If you're lucky the contacts to the battery will still work and since you removed the 470ohm resistor already that will restore full functionality of your board (check
Xian Xi's battery mod tutorials).
Good luck! If you run into more trouble and need that MV1FS you sold me back, let me know and we'll work something out.