I always thought that though Trow cannot reproduce, they would have been able to maintain their number.
Tharsis is called the Forge of the Trow, this means 3 things
1. This is where the Trow could have forged their iron weapons of yore
2. This is where nyx created the trow
3. (What I think could be a possibility) I think this is where the trow, pick up the old crumblies of trow, and melt them into new trow. Remember Trow not only used Iron but they are made of iron. (another reason they felt bad about using Iron weapons... Would you use weapons made of human flesh against your own brothers?)
