I seemingly got you a bit wrong, sorry 'bout that. Windows 8 comes with Bluetooth drivers by default. If you have had it running with Windows 7, there shouldn't be any problems. But as always, new systems come with new problems. A lot of problems reported with Windows 8 Bluetooth...
BIOS isn't really the issue, it's more related to basic hardware, and management of those, and voltages and such. It rules the basic functions of your computer before Windows step in picture. Taken mainly, you don't really need to mess with the BIOS at all, it's practically "everlasting", unless you want to tune it, and that's quite theoretical. I do update my BIOS, but it's highly due to vanity, I just somehow want to be "on the edge" - whatever that means...
The Bluetooth should not be lost, but I strongly suggest you save everything you have. Preferably on a separate disk, USB or, XD, SDHC, SD, compact flash, Memory Stick Pro Duo, Micro M2 MMC, micro-SD, Mini-SD