Number one question: has your organic traffic also fallen off a cliff? Go to Google Analytics and answer this question immediately.
Just because the Moz rank tracker shows your rankings slipping doesn't necessarily mean the keywords that you told it to track are the same keywords that drive all the traffic and/or revenue for your site.
Hopefully you'll find that your organic traffic is holding steady and the keywords you thought were important enough to put into the Moz rank tracker aren't the same ones that drive traffic for your site.
HOWEVER....
If you find that your organic traffic has ALSO fallen off a cliff then you've got bigger problems. Without knowing the site or anything about what you did in the past couple weeks my first gut instinct is that all those duplicate pages you took down had good natural links to them and were therefore the ones ranking for your keywords.
You should have 301 redirected or canonicalized those pages rather than removing them completely. I honestly don't know what would happen if you just put them back up and pretended like nothing happened, then got to work properly redirecting them to the pages you want to rank.
So I would recommend the following steps:
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Consult Google Analytics (see above)
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Plug your site into Open SIte Explorer. Look for links to pages you have since taken down. If you find lots of them then you know what your problem is.
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Consult with someone with more technical expertise than me about putting those pages back up and then properly redirecting them