Same Thing happened to me
You have plenty of options.
Mywifi died and also needed a logic board replacement to fix it, here is what I learned from my experience.
There are many usb wifi options out there that work for mac. In fact, most of the products use one of a couple different chipsets. And the manufactures will have a mac driver even if they may not say mac on the box.
I'm using a TP-LINK (TL-WN823N). This one was a little annoying, The driver on the tplink website won't work on Yosemite. You have to go to the chipset manufacturer page to get it.
Realtek <-- Manufacture RTL8192CU <-- chipset #
osx 10.8 Drivers worked for me on 10.10
Drivers:
Realtek
Other options, I have not personally tried but should be easier than what I did:
Edimax EW-7811Un 150Mbps Wireless 802.11b/g/n... in stock at OWC
OWC has other usb wifi adapters that should work as they sell mac only products
I like the size of this one
The Edimax provided driver should work but here is the chipset (as you can see it's just realtek again)
Realtek RTL8188CUS
Here is a comprehensive list of specific USB wifi adapters for hackintosh and will work for a normal mac.
The Best USB WiFi Adapters For Your Hackintosh
There are also many more that will work you have to go to the company page and see if there is a mac driver. They never say osx on the box. For example D-Link DWA-171 is not advertised for mac, but you can select mac on the driver download page.
DWA-171 Wireless AC Dual-Band Nano USB Adapter | D-Link UK
^^Once More it's a realtek
Realtek RTL8811AU
Ethernet solution - No driver required:
This is what I almost got I did a lot of research on it and seems like a great solution.
I got my off brand wifi usb to work with yosemite so I didn't get it.
This one will do up to 300mb/s (same as your old internal)
WNCE2001 | Gaming & Home Theater Adapters | Connected Entertainment | Home | NETGEAR
This will do up to 600mb/s (your built in was up to 300mb/s)
WNCE3001 | Gaming & Home Theater Adapters | Connected Entertainment | Home | NETGEAR
They both can be powered over usb or ac wall adapter.
Best buy keeps these in the home theater section.
Intended for putting your ethernet enabled TV on you wifi.
Benefit here is they will keep working regardless of how apple changes osx.
with a usb you might have to wait for a driver update.