Najan, Sorry to hear you had such a disaster with your PC. I've never had anything like that happen to me, or have seen anything like this.
After looking at your pictures, particularly the second picture of the bottom of the CPU, I have a few comments.
The rectangular area at the center of the CPU, which only contains capacitors, is clearly damaged by heat or burning, several of the capacitors seem to have literally melted or have detached from their connection points as if the solder melted.
The electrical contact points on the CPU (known as the substrate land's) seem to have indentations on them, apparently from the contacts in the socket. While you can clearly see that the socket contacts have left marks nicely centered in the CPU substrate lands, I have never seen indentations like that on any CPU's that I have. Another thing that is strange is that there are two areas in the socket where there are no contact pins, which can be seen in Figures 3-2 and 3-3, and described in section 3.1 of this document:
Given that, I don't understand why there are indentations on the CPU substrate lands in the areas that correspond with the areas on the socket that do not have contacts. The indentations on the CPU substrate lands can be seen on almost every land in the second picture.
After examining that second picture, and checking the document in the link above, IMO it seems there was a problem with the socket, or possibly excessive pressure on the CPU for some reason.
I think it states in the CPU warranty that the use of an after-market CPU cooler can void the CPU warranty. Is there anything in particular that is causing you to think the CPU is the problem, rather than the mother board?
I'm surprised that the retailer that sold you both the CPU & motherboard didn't replaced both of the (2) parts. Both parts are under manufacturer's warranty so there's really not much of a question of returning it. Customer's satisfaction is guaranteed or your money's back as long as you purchased it within a specific time frame clearly written in front or at the back of your receipt (usually 14 days for electronic stuff). You could have just walk straight to the customer service & return the products or have it replaced. Simple as that. You don't have to call Asus or Intel to have it replaced. That's the job of the retailer where you purchased the deffective part &/or parts.
Some retailers even provide (for a small) fee a replacement product if that product gets destroyed as a result of voltage problem or overclocking for the entire 3 years (past the manufacturer's warranty). I got my Core i7 2600K CPU with warranty protection ($29.99) that I've purchased at Micro Center.
Having the retailer test the parts to determine which part is defective is not really the wise thing to do. You have the option to return the product when it's still under the retailer's warranty. Next time go straight to the customer service & return the product. You don't have to justify yourself. Tell them that you're not satisfied of the parts that you purchased & you think it's deffective. You tell them you want to return them or have them replaced with a similar or if you opted, for different product &/or products.
I purchased lots of stuff over a decade & my experience tells me that it's not really that complicated returning stuff you don't like as long as it's within the seller's return policy. As long as you return it while it still can be returned then there's shouldn't be any problem.