If Rage was done correctly, it would not end until the start of your NEXT turn, if you didn't attack and were not damaged at all during the *entire* next round.
Thanks for that information. I wasn't sure if I misunderstood how rage worked or if the tooltip was wrong : "Rage ends early if you haven't attacked a creature or taken damage since your last turn." Fixing how rage ends would make Unrelenting Ferocity actually useful during combat, which mostly solves my problem.
That "end of combat window" still exists, though. Aside from the Bearheart barb example, where exploiting that window is the only way to use Unrelenting Ferocity, I'm sure there are plenty of interesting ways to use it. Maybe it's the last few turns of Featherfall and the party needs to jump to a lower level before it runs out. Maybe you want to try a skill check with a Blessed PC before the buff is gone.
I've tried going into turn-based mode immediately after combat, but that doesn't work at all. The game waits for 10-15 seconds before pausing the world, by which time it's too late for shenanigans. Maybe things run more smoothly with a better computer (the wonderful folks in this forum can enlighten me on that score). Still, I wish the game acknowledged that the tactics don't end with your last foe's last breath.