Micarta is tough as nails. It doesn't have quite the compressive or tensile strength of G-10, but it is tough enough for anything that I'll throw at it. If I'm putting enough force on it to damage it, I should probably be worried about getting hurt myself!
If you go look up the manufacturer's technical spec sheets for G-10 and C-grade phenolic, neither one absorbs much moisture over a 24 -hour soak period. G-10 will absorb around 0.10% of its weight in water, while canvas micarta will absorb 0.75% of its weight in water. Neither one degrades significantly with exposure to water.
TedP