Disclaimer: If you're an early return of fertility girl, vaya con Dios.
Your humble blogresses have been negotiating off-blog the swampy terrain of lactational amenorrhea/anovulation. We have our reasons. :D Here are two ways I inform my approach (girls, this started as a reply to you, but I figured if all three of us are thinking about it, surely our tens of thousands of readers are too):
1. Way back when, my husband spoke to a Venerable Hausvater about such things. This VH shared that his CSPP-Professed nurses the current baby until she's pregnant again. I'm not sure I could promise to keep up that long if I went for a really long stretch without getting pregnant, but I find the overall principle, coming as it does from such highly Venerable types, reassuring. (Not much help for those who DO NOT get pregnant while nursing, though.)
2. My husband also reminded me when I went looking for his thoughts on the matter that in Starck's prayer book, the prayer for a mother of a newly weaned child begins with an explanation along the lines of, since the time of weaning is the time when the child begins to go out by himself . . . . Taking the long historical view is always of some (and usually of great) value, and child care is no exception. (Incidentally, Blessed Martin Luther is on record offering lactation advice to Katie [ctrl-f "weaned"; Baby Magdalena was 14 months old]. My husband has long maintained that any husband worth his salt is an expert on lactation and much more credible on the topic than anyone Board Certified.)
I don't think Concordian Sisters need to feel bad about hanging around in the frying pan for a while before diving back into the fire. Either way we're plenty crispy. In my own life, the fire has been the less infernal option a few times, and I went for it. (Hard to believe, since we all know breastfeeding isn't painful if you're doing it right you stupid idiot. At least I stuck it out for the requisite year to keep myself off the IBCLC's Maternal Failures list)
If Mom and Baby (especially Baby. And especially Mom) are both happy nursing, nurse. Better not to think, "If I nurse the baby until X I won't have another one until X+9." Better to think, "I think we'll keep nursing today" or "Maybe we'll try to skip that feeding today and see how it goes."
If your baby still wants to nurse, I don't think it's a good idea to wean just because you doubt your own motives for sticking with it. You go can go to confession, but s/he can't go back to nursing (if you're hard core enough to think s/he can go back to nursing, you probably aren't considering the weaning question to begin with).
This all makes me think we might be better called Concordian Sisters of Perpetual Lactation. We don't always have a baby countdown for you, but I don't think we'll ever have a time when that nursing sticker will need to come down.