Unable to boot up my Mac. Getting a flashing folder with a question mark I currently own a 15 inch MacBook Pro with retina display model ( early 2013) . My Mac was working fine and all of a sudden my Mac won't boot up. I see a flashing folder with a question mark symbol on my screen.

I took my Mac to a technician who diagnosed the issue and said flash disk has to be replaced. He said  "Reseted SMC and PRAM. Still same issue. Tried to erase the SSD by booting with known good OS. still same issue. tried to erase the SSD using terminal mode same issue. tried to repair the SSD found not getting repaired. Reseated the SSD and tried to erase the SSD still not able to erase the SSD".

Is there any other way to fix this issue without replacing the SSD? 

Or could you suggest any other SSD for this model of Mac?
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.