i can pretty much assure you that you won't have any problems going back to california from chicago....everyone i know here who wanted to go back to CA got jobs in whatever market they wanted (and that includes a few people i know who were around bottom 10-20% of the class). i had several offers in silicon valley and i'm nowhere near the top of the class.
is duke giving you $60,000 per year or total? if it's $20,000 per year, i would probably do chicago. if it's $60,000 (so basically full tuition) per year, it would be a pretty tough choice.