Recovery should work but in may take a long time depending on other calls on the CPU, RAM, size of the d/b. From expereince, it’s very difficult to predict how long a recover may take.
Let’s assume it won’t recover. My next suggestion is to make a custom ‘Catalog Type’ based on you current catalogue (or one such per catalogue if they use different customisations. Now make a new catalogue based on the set and drag across all the records (if many, doing so in batches of c5k records can help with performance). Saved views can be exported/re-imported but Saved Finds and (Smart) Galleries will need to be rebuild from scratch. Previews too, will need to be rebuilt as record ID #s change when the records are dragged across.
v10 will open v8.5 FDBs, so you can either open the originals or rebuilt one: note that doing so is a one-time update after which the FDB can’t be used in v8.5 (so work with copies). Or make a new catalogue using the custom type in v10, open the old v8.5. one (better, a copy thereof) and then do the migration of records.
FWIW, you should be able to recover a 2 GB FDB assuming enough horsepower and the catalogue doesn’t have bad corruption. The only real limit I’ve hit is someone who’d made a 4 GB FDB (the biggest you can make) and it was too big to recover.
Hopefully that gives you a few options.