Given your 1-inch of "trashed" fiberglass, leave it in place temporarily, cover the patching area with Saran Wrap, and build a new backing with a couple of layers of cloth and resin. After it's cured, remove the new backing from its Saran Wrap "release medium". Trim as necessary the "trashed" area, allowing enough space to slip the new backing patch behind the formerly "trashed" area.
Prepare a bed of thickened epoxy, install a screw-eye to the middle and bungee the new backing firmly into place.
Fill, Fair, and Finish.
Pretty much my current plan, I just never liked the backing held on with just thickened epoxy. As long as there is enough glass overlap on the inside it should be strong enough though.
Each quarter-inch bump of "solid" roving material is surrounded by a tiny bit of brittle gelcoat. (The smooth gelcoat you can see on the deck's seen surface).