Just my 2 cents since we're all stuck in the newbie section together
You've already invested the cash. If you really don't think bitcoins will come back, then quit mining and call it a loss. But if you think the price will go up, maybe not to previous levels but at least to profitable levels, just keep mining and hold coins til later.
True investing isn't about quick returns. If this is an investment than you have to look at the long term process.