I've done a fair amount of veneer repair, re-veneering and veneering on boats and furniture. It's really not all that difficult to renew even badly delaminated panels. (Furniture is a different problem since the glues are most often not waterproof; it requires working over water-soluble glues with new water-containing glues - you're likely to damage the old bond adjacent to your new work.) I think that glues in marine plywood are likely to be urea-formaldehyde and while the stuff is pretty good, it gives up with repeated wetting/swelling and drying/shrinking of the veneers. You can glue to uncleaned surfaces of this glue with epoxy.
The face veneers are usually quite thin, and usually more rot-resistant than the core veneers. If the face veneer is intact but the core is rotten, you can remove the panel and repair from behind. If you're lucky, you can dribble epoxy into the delaminated edge and then clamp to a flat surface. You very gently cut rotten core veneers from behind and replace them. Work on a flat surface. Clamp your new work to that flat surface with a plastic no-stick sheet; epoxy will always find a way through the veneer. Then refinish the whole panel. Additionally, I coat the edges and the back of the panel with epoxy so that the inevitable next leak does no damage. See a bunch of pics in my album 'Repairing Veneer'.
