[Immaculate]

For the record, i attacked an indi province with 2 commanders and 30 something units. I lost - retreating only 1 of my 14 units. But the battle summary said that i killed 2 of the 2 commanders. Next turn i attacked with only 1 commander and i won.

So all to say...

if you kill the indi commanders but lose the battle, you can take it next turn regardless of the number of troops remaining (at least in this case).