iMac mid 2011 doesn't boot [duplicate]

Take a look at EveryMac's Retina MacBook Pro page here. There is valuable information regarding compatibility (or lack thereof) of SSDs between different models, options for 3rd-prty upgrade offerings and lots of stuff you generally need to know about SSDs for Retina models.

Dealing with your actual problem at hand, SSDs aren't difficult to test, and any decent technician should be able to diagnose the issue. If your technician says it's died then by all means get a second opinion but SSDs have the capacity to fail like any other electronic or mechanical component.

If you're an EU resident you may have a case for a free replacement from Apple as EU-wide consumer law forces companies to offer a 2-year minimum warranty period. Getting them to honour a warranty may not be easy but it's another option. You never know, you could get lucky and find someone sympathetic to your plight who's willing to swap out the defective SSD.

The flashing folder with question mark means that it cannot find the OS to boot to. When you boot from a CD/Flash/USB Device it means that your MacBook is still functioning and the problem is limited to the drive and its related subsystem.

So, you are down to two distinct components that could be the problem with your Macbook: the SSD or the SATA controller.

The SATA controller is part of the whole logic board and cannot be individually replaced so if that is the problem, you will need a new logic board.

What the tech is saying is a little "half-arsed" in my opinion. He is basing his diagnosis on the fact it is the easiest thing to replace. To know this for sure, he needs to swap out your existing SSD into a known working machine and/or a known working SSD into your machine. That will tell you if it is your machine's logic board or its SSD.

Throwing parts at a problem is just expensive and fool hardy. Depending on the age of the MacBook and your AppleCare warranty, this all may be covered. If not, it will be a moderate cost to replace the SSD (if possible) and almost monumental to replace the logic board.

If it is the SSD and it can be replaced, now would be a good time to upgrade to a larger size.