Hey everybody, I thought I would share my experience troubleshooting corrupted save files on Mac OS. This will be pretty quick.
Basically, I've discovered that quitting the game with the Command + Q keyboard shortcut creates corrupted save game files, resulting in the "Continue" and "Load Game" options being greyed out on the main screen. Which files it corrupts seems random to me, because sometimes deleting older save files seems to fix the issue. It seems like the further you are in the game, the more likely you'll start seeing this. I began seeing it in what I believe is Act 2.
So first, only ever quit the game with the in-game menu, and second: Use Time Machine or some other automatic backup system. If your save games are suddenly corrupt, replace everything in the save game folder with files from right before you lost the "Continue" option ( ~/Library/Application Support/Pillars of Eternity/Saved Games ). Failing this, I recommend deleting older save games one by one until the continue option is selectable again.
I hope this helps someone!