Really not much of a challenge.  I did just this (involuntarily) last month, and it really wasn't too painful.  My Retina MacBook died (the backlight would come on, the fans would spin up, it got hot, but other than that it did nothing) so I took it to Apple for repair.  That took a week.  Given that I've given my Air to my wife, and my BlackBook to my mother, I needed a notebook for work. That left only my old 667MHz TiBook, chipped paint, dents and all.  It started first time - and, after a few hours plugged into the mains, it even retained a charge. 

Sure, it was a little slow - but I was able to load my core work tools (Safari, BBEdit, Microsoft Office, Xcode (in a limited fashion) and iTunes for Music).  I had to wait until the Retina was back before doing any Windows compiles - but other than that it was fine.  

I'm kind of used to these shenanigans anyway because I use my SE/30 for preference for text editing and even some shell scripting (woo! A/UX!).  I find the little 9" screen very work-friendly.  It's so small that there is absolutely no temptation whatsoever to load distractions into other windows.  Just the one work window, no messing.