You got a free upgrade to a golden legendary, so not really much of a mistake. You’ll just only make a profit of 400 if you dust your regular Leeroy, where as if you dust golden Leeroy you’ll make the same profit you would have keeping regular Leeroy but for far more investment.

Not true. When Mind Blast and Vanish rotated out they were converted to common cards and you were given a dust refund.

There’s no reason why the same won’t happen for Divine Spirit and Northshire Cleric. They’ll be converted into commons and you’ll get a refund for them.