I went back to work at 10 months, and actually never pumped. DS drank H20 only, and actually wasn't eating a lot of solids. He nursed like crazy all night though
DS is 2 1/2... still going strong.
I have an aunt who went back unexpectantly at 3 months (her dh died) and her ds refused a bottle. He would just drink water while she was at work (~8 hours/day) and breastfeed like crazy at night. Her ds was 3 1/2 before he quit.
I have another aunt who taught school (went back at 6 weeks) and couldn't pump (nice progressive school, huh?) and bf for over 2 yrs.... another cosleeper/night nurser.
I think the big thing if you want to stop pumping and maintain supply is night nursing/cosleeping. That, in my humble opinion, seems to be the biggest factor in determing how long the bf'ing relationship continues.
As far as a milk supplement, I guess I don't necessarily think you have to give your child some sort of milk (besides yours of course). You can get all the good stuff in foods like yogurt which is a lot easier on the digestive track as far as dairy foods go and just give water.
Trust your instincts.... and DON"T WORRY!