Loss of galvanizing will not result in loss of strength. Over time the rusting will lead to loss of strength as the section of the chain link is reduce. In the short term, 4-12mo, there should be no significant loss of strength.
G4 chain depends on the steel
formulation for its extra strength relative to G3/BBB so the heat of regalvanizing will not affect strength unless the zinc bath is serious over-heated. Higher grades of chain are heat treated and will lose strength when regalvanized.