According to a post I read, you can downgrade your BIOS to an earlier version. You can read what the person said here:
Some computers allow you to downgrade the BIOS, while others don't. Apparently this person was successful in doing this.
If you can downgrade the BIOS, that is definitely the way to go. Changing a motherboard is major surgery on a laptop. (On a desktop also, but especially so on a laptop.) There are lots of tiny, fragile things that can easily break when you are doing this. Tiny screws can get lost or mixed up. And you can easily short something out with static electricity by touching something with your bare hands.
If you decide that you need to replace the motherboard, then watch several YouTube videos about people swapping the motherboard on the same laptop that you have, before attempting it yourself. Also, see if Asus or anyone else publishes instructions for replacing the motherboard on your laptop. Having instructions is invaluable, and I would not proceed with changing the motherboard without having some instructions, if it was my first time to do so.
You will need an anti-static wrist band. Something like this:
You will also need some cleaner, some q-tips, and some thermal paste (see below), a can of compressed air, and plenty of table space.
And you will need a new CMOS battery to replace the one currently in the laptop.
You should also get a poster board and a note pad. The poster board is for putting screws and other parts. When you do step 1 (for example, remove the back cover), you will put the screws on the poster board and draw a rectangle around them. And write in the top of the rectangle, "Step 1 - screws from the back cover". You will also write down exactly what you did on your notepad: "Step 1 - I removed the back cover. There were 12 screws. etc." And take plenty of pictures, and maybe some videos of things, because you can record your voice in the video: "Step 1 -- I removed the back cover. These two screws were big, the rest were small" -- and you will point to those screws in the video. You may not need all of the pictures and videos, but if you do, they will be a life saver.
As you are proceeding, move slow, not fast. Be super careful in everything you do. And don't force anything. If it won't disconnect easily, then you aren't doing it the right way.
When you get to the CPU, remove the heat sink, clean the surface of the heat sink and the CPU with cleaner (Arctic Silver ArctiClean), apply new thermal paste (Arctic Silver Thermal Paste) on the surface of the CPU, and reattach the heat sink. Blow out all dust with a can of compressed air.
Change the CMOS battery while you have the laptop disassembled.