Replacing wood on 24" center trusses

Trusses 24" on center and builder used 3/8" plywood. Plywood is now delaminating and soft in spots. Would like to rip off all of the wood and use 1/2 or 5/8". Just not sure that the weight would be too much? Also, half of the house is cathedral ceiling. No ridge vent installed originally. Do ridge vents suffice in cathedral ceiling area?