When I went back to work and I was pumping on schedule during the day, during the night-time hours, if I didn't co-sleep and let baby nurse at will throughout the night, I did get up at least once in the middle of the night to pump and would then pump again before heading off to work.
For all of my children, I nursed up to a year. I co-slept/nursed until they were about 6 months and then moved them to a crib when they started solids and sleeping through the night.
But back to your question, I think if you're "well-established" and more importantly, you get adequate time during your workday to make up the difference in pump-sessions, you could probably get the extra sleep.
The key with keeping your supply up, is making sure you pump and/or breastfeed several times during the day so that your body doesn't "think" you're begining to wean. My little formula for success (especially when I was working) was being sure to pump no less than every 3 hours for no less than 10 minutes on each side (even if very little is expressed). I was lucky enough to be less than a mile from where I worked, so I breastfed the baby during my lunch break. And then exclusively breastfed during the evening hours, letting the baby nurse for as long as they wished, and as often as possible. The pumping was really reserved for times I was away from the baby. But when I was home, pumping took a backseat, and I offered the breast whenever possible. The natural way to feed a baby will always trump pumping. The machine can not express anywhere as much as your baby can, and this is where the risk of diminishing milk supply lies.
So if you want to keep supply up, feed naturally whenever possible. Look at pumping during the work day as a way preserve backup supplies and to maintain the "factory's production" if you will.
As I mention earlier, one very good way to ensure you still get sleep, but can continue to feed the baby throughout the night is by using the "co-sleeping" method. If you and your dh don't mind sharing the space with your little one during the remainder of her "nursing months" the baby can nurse at will during the night. There are lot's of books about night nursing. Go to www.lalecheleague.com and check out the many titles they sell on the topic. The most comprehensive of their books is "The Womanly Art of Breastfeeding" and this topic is addressed. You might also find stuff on their website.
The great thing about co-sleeping and nursing is (as you will learn if you research this more) that your body is it's most productive (milk-wise) when you are at rest (deep sleep) and within a short period of time you will produce milk abundantly. It's also a great way to bond and make up for the time away from your baby while you've been at work.
Hope this helps.