I nursed well into toddlerhood. Since we did child led weaning, it was a low slow taper. I didn't notice any weight change.
I imagine if one is weaning at the year or in that neighborhood, it would be more dramatic a change.
For us, it isn't like toward the end she was taking in lots and lots of milk -- my production had gone way down and it was like the 5-10 min nurse right before bed that was our only nursing time. What could that possible be? A few ounces at best? Certainly not anything to note on the scale.
I did the same as "astrophe" I nursed mine till they were 2.5 yrs and they self weaned, I never noticed a difference. As they started weaning my supply went down gradually till I was dry.
I nursed my three for just over a year each, and each time I was able to lose the baby weight (from the 160s down to the low 130s) while I was nursing. With my third, I lost the weight by the time he was 7 months and I was still nursing quite a bit (with the first two I didn't lose the last few pounds until later, when they were nursing less).
I'd echo what is said here, and have the experiences of hundreds of breastfeeding mums to go by. If you wean quickly when you have a high milk production, you will notice a bigger drop. However, its not likely that you are holding on to the weight, as much as the breasts themselves have stores that will shrink. So if you see a 5-10 pound drop, you might notice it more in the bra than in the waistband.
With my first I struggled to lose and I nursed her for 22 months
With my second I lost weight easily but regained some when I weaned at 26 months. I had a hard time compensating for the calorie drop. It was slow weaning over a year in which I gained slowly and then a big jump a month after I weaned completely.