Same here on Raspberry Pi 3 B, Raspbian Stretch, firmware-brcm80211 20161130-2.
Getting brcmfmac43430-sdio.txt (and brcmfmac43430-sdio.bin) from https://github.com/RPi-Distro/firmware-nonfree/tree/master/brcm80211/brcm makes Wifi work again. See also https://www.raspberrypi.org/forums/viewtopic.php?t=150543
