Water Damage Diagnosis Followup

While you do appear to have some damaged parts here (the cable), you also have a lot of corrosion built up around some of the components.

I would start by cleaning up as much of the junk first and then see where you are.

I would use distilled water (not tap) with cotton swabs and a toothbrush to clean things up first. Just be careful you don't snag or pull off any of the smaller components. If the water alone doesn't clean things fully try using a solution of distilled water and baking soda (about a teaspoon in a half liter of water). Then afterwards wash the area again with the distilled water to remove any traces of the soda. Then you will want to use good grade of isopropyl alcohol (85% or better) to clean down the areas again to remove any grease or oils and to act as a drier to the water that has likely seeped under the components. I would recommend letting the logic board dry out letting the sun warm it for a day before trying to power it back up. In its self it won't undo any electrical damage but is can make sure no more damage progresses.

I did note you have some damage around the two FET transistors near the battery connector. Hopefully the traces are still good under them. They may need to be replaced if they shorted out (likely from the corrosion).

As to reflowing I would hold off on that as that may not be needed.