Default Flashing/Mobo/SDS questions

Not sure if this is in the right place but here goes

So I woke up this morning to my phone not turning on past the bootup screen, checked the battery, thats not the issue. A quick google search led me to sudden death syndrome where the mobo just dies. I want to replace it. Thing is, my phone has already been flashed from sprint to boost. I am wondering if by replacing the mobo, do I lose this flash? I noticed when looking for new motherboards on ebay etc that they are listed as bad/good ESN, does this matter for me seeing as my phone had already been flashed and all I am replacing is the mobo? Or will this upgrade necessitate a new flash.

Thanks in advance