Of course, you'll be able to leave formula for your child instead of breastmilk. I am concerned about the fullness of your breasts by the end of the day, though. Since it's only two days a week, and from your post, it sounds like you'll be nursing the rest of the week, your supply probably will remain the same on the weekend as it does during the week.
You'll need to find a way to remove some milk from your breasts at least a time or two each day. You can use a pump, of course, but there are other options.
You can express your breast milk manually, see instructions here. http://www.lactationinstitute.org/MANUALEX.html It can take practice to master this, so you might want to try it at home, or even in the shower.
This technique is good because you can express just enough milk so that you're not engorged, and you don't have to worry about keeping it. You can express the milk into a cup, bowl, sink, or whatever's available.
You can take a few minutes to do this only when you feel like you need to, not on a schedule.
If you decide to go back to work, know the signs and symptoms of plugged ducts and mastitis, so you know what's happening, and what to do about it, just in case it happens. Plugged ducts are much more likely to happen when you're not emptying your breasts as often as they're used to be emptied. Read about it here: http://www.lalecheleague.org/FAQ/mastitis.html
Only you can make the decision that's best for you and your family. If you want to try it, see how it goes, then re-evaluate your plans for the next weekend. It will all work out in the end. :-)
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