> If the veneer is damaged or sealant ruined and not resealed it could seep in water from the nearby sink, causing more damage and repairs to complete.

But that's the thing, the countertop is well sealed right now how it is. The sealant just went deeper where it was sanded more, so the color is off. If OP sands everything down with the higher grit sandpaper to reseal everything, the veneer will get thinner and if a future reseal is needed there is a bigger risk of sanding through it.