Well I can't offer any advice as my baby is only 12wks, but I do want to say well done for b/feeding to 1 and beyond, especially with the others giving up. I find it very odd that people are suprised when you're still breastfeeding a 1 year old when they fully expect that if bub was bottle fed they would still be having a bottle at that age??.
Your supply might drop off, but someone correct me if I'm totally wrong but my pregnancy/baby book says that at 1 they don't absolutely need breastmilk since wide variety of solids by that age, so even if if supply drops off it's not a big deal if you want to just feed with the milk you do have and comfort. Good Luck with returning to work too!