do we just lose it or does it get converted into gold?
No, that is not happening 
I can tell you that much
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From what I read, it is essentially lost or converted into cosmetic stuff, so best use it all (furniture and so).
Would be nice though 
Each of your characters should get a bag of gold (like 1-2k at least) like we did after MoP Remix. But yes, would be nice if Bronze did convert to gold. There’d be a few more millionaires I bet. 