So I have had this issue where my wireless card would one day suddenly disappear. I had a wireless usb so I used that for a month or so and finally I decided that I would just reinstall and see if that fixed it. It did like magic but then a couple days later poof gone. Now if you are reading this there is a good chance you have search for linux and broadcom related information and you have found a ton. Ultimately I fixed mine using information from a few sources:

First you can list your network related hardware using:

$ sudo lshw -C network

Confirm that you have a broadcom chip. In my case the broadcom chip was listed as "*-network UNCLAIMED". Next you can check for some sort of blocking

$ rfkill list all

In my case before I fixed the issue my wireless device wasn't even listed. After that I would run:

$ lspci -vnn | grep 14e4:

In my case after finding that command I check back on the table at http://linuxwireless.org/en/users/Drivers/b43#Supported_devices. My device was listed as 14e4:4727 which is BCM4313 (same as lshw listed) Next I looked at http://linuxwireless.org/en/users/Drivers/brcm80211 I found my chip in a table listed under " brcmsmac" from my research I knew that "brcmsmac" was one of the options for broadcom drivers. So I tried modprobing it as I had done for 'b43' and 'brcmfmac' earlier.

$ sudo modprobe brcmsmac

And success!

Lastly if you don't want to run that command every time you turn your machine on you could add "modprobe brmsmac" on a line immediately before "exit 0" in the file /etc/rc.local

The four most helpful and complete sources: https://wiki.archlinux.org/index.php/Broadcom_wireless#broadcom-wlhttp://linuxwireless.org/en/users/Drivers/brcm80211http://linuxwireless.org/en/users/Drivers/b43#Supported_deviceshttp://askubuntu.com/questions/235279/my-wifi-adapter-is-not-working-at-all-where-to-start-troubleshooting