ok, I couldn't wait any longer. after a test with another drive I found the following solution:
1) Delete the failed volume
2) Ignored the warning about it deleting all the data on the drive blah blah blah, and continued to delete the volume
3) Once the volume was deleted the drive was available as just a regular drive with all my partitions and (as far as I can tell) my data intact.
4) Copied the data off
5) Job done
This worked for me (twice) but I can't guarantee it would work for anyone else, so try this only as a last resort at your own risk!