I'm only 20 and having kids is a ways away for me, but I've thought about what it would be like if my child/ren had bpd. It would be difficult, but I personally think the gift of life in itself outweighs the damage of having bpd. Also, adoption is always an option. I may choose to adopt in addition to having my own kids. Yes, the prospect of raising someone else's child, who could come with unknown baggage and medical issues, in addition to my own bipolar kid/s, is daunting, but I guess I'll see when I get there.
And, of course, there's always the large chance that your kids will be completely free of bipolar disorder.