You should easily be able to find out the amount for which the lender purchased the house at the sheriff's sale by contacting your county clerk's office. The difference between the amount of the sheriff sale purchase and the amount you owe on the defaulted mortgage is the amount for which the lender may seek a deficiency judgement. They will have 6 years in which to seek this judgement and seek reimbursement from you. Obviously, your credit record will be dramatically impacted for the next many years as well.
In Michigan you have 6 months from the date of the sheriff's sale in which to "redeem" the property which basically means that you can pay the back payments, fees, etc. that are due and then be able to continue with your mortgage. You have likely been receiving formal notices telling you the amount that is owed. If you are truly interested in redeeming your property, I suggest you consult a good real estate attorney.
You are correct to be suspicious of those seeking to "help" you by having you sign a Quit Claim Deed. I see absolutely no advantage to you in doing so. Your deficiency has been determined by the amount of the purchase at the sheriff's sale. If you are seriously contemplating such a move, you should seek the advice of a good real estate attorney.
Unfortunately, although you decided to strategiclly default on your mortgage obligations, you may find yourself looking over your shoulder for 6 years waiting for the lender to seek reimbursement for the defaulted amount. There have been a number of publications indicating that lenders are anxious to make examples of those who have strategically defaulted on their mortgage obligations.
This is a very complicated situation and you will be unable to receive full and complete information from this type of forum. This is the time to seek assistance from a real estate attorney if you are truly concerned.
Best of luck to you,