Logic Board Reflow Question

As the others have mentioned, reflowing the board will only fix bad solder joints, not water damage. Water damage will typically cause shorts which can fry components.

Depending on the component, the damage won't always be visible or obvious. If you see a capacitor or resistor that looks dark or warped, that may be a candidate for replacement and be worth a try if your part hunting and soldering skills are up to snuff. But that still won't tell if you if all the complex gates and circuitry inside the larger chips is working properly. With those components, there's really no way to know without sophisticated and expensive equipment and an Electrical Engineering degree.

If you don't see anything obvious or the computer still doesn't work after replacing basic components that look damaged, you're probably looking at replacing the entire logic board.