Hi,

if you bend one of the remaining foam battens and compare the stiffness (the curvature) with that one of the glass batten and you see a significant difference, then it will slightly degrade the performance of your boat.

Regarding complete replacement: If you have a workshop, you can build foam battens your self. For my battens I took a wood strip as core and laminated uni directional glass on both sides. The epoxy resins protects the wood from moisture. It was about 3$-4$ per batten and works fine since two years.

Cheers,

Klaus