What RF were you using and had you been running repair regularly ?
RF 1 *sigh*. Waiting until I have more/better resources to use RF > 1. Hopefully soon.
In the mean time... Oddly (to me), when I removed the most recently added node, all my rows re-appeared, but were only up-to-date as of a 10 days ago (a few days before I added the node). None of the supercolumns since then show up. But when I look at the sstable files on the different nodes, I see large files with timestamps in between that date and today's, which makes me think the data is still there. Also, if I re-add the troublesome new node (not having run cleanup), all rows are again inaccessible until I again decommission it.