When I had a motherboard issue with a dell laptop, Dell sent a representative to my home office to take it apart, clean it, and replace the motherboard.
I've also had laptops and monitors replaced by other companies on a "we'll send you a replacement, you send the defective one back in that box with this prepaid shipping label, and thanks for buying our products" basis.
When the G5 iMacs had problems with bad capacitors on the motherboards, Apple would send you the replacement midplane with swap instructions, along with a box to return the old one in.
I've also had laptops and monitors replaced by other companies on a "we'll send you a replacement, you send the defective one back in that box with this prepaid shipping label, and thanks for buying our products" basis.
I haven't heard of that from Apple.