Not to turn this into "Cowgirl should have a baby" thread, but for how it works for mom going back to work, I gotta be honest, with our first, dad went back to work before mom, so dad learned to sleep thru stuff...but not mom elbowing him and asking if he'd please take duty because mom was shot...and dad was glad to help then...even if I was going to be tired tomorrow. Baby sleeps, daddy sleeps. With our second, it was easier, because mom only went back part-time.
However, think of your mentions of sleepy little peanut...imagine that...but your OWN kid. That's how you get thru. There are times you are ready to fall over, there are times you wonder what the hell you got into, but if you do it right, sometimes in those times your spouse is there to step in, and sometimes you just gut it out.
My oldest just turned 4 yesterday (thursday)...and watching him ride his first pedal bike is worth all the missed sleep...which still happens because 22 month old still likes to get up at like 5:30 in the morning....and if you do it right, you can also get closer to your spouse. For all my snarky, sexist humor on here, my wife and I just sometimes serve each other. I may not want to do something, but I know that getting a load of laundry done or making sure she doesn't have to worry about dinner is how I can show her I love her today. *caveat: If you do it wrong, it can ruin things just as easily as it can make things great, so you gotta be in a good place to start. "We were having some troubles, but I thought having a baby would fix everything" is the dumbest thing I've ever heard.