The seller has multiple remedies to get the property back in case of default.  

Do you about what to look for to avoid or remedy these?

My advise is to immediately start getting the place ready to re-rent and advertise, and simultaneously get a lawyer (or yourself) to send an official letter outlining everyone's responsibilities and remedies.

The house had about a foot of water (just below the outlets) and the owners took the appropriate measures to have the house dried out and mold remediation done.  

They even complained on one that the local chipmunks and squirrels had eaten their plants in the garden (complete with photos of chewed plants) - and the remedy they sought for each of these filings was termination of the lease.

Nonpayment of rent by tenant: Landlord's remedy.

Plus, from another aspect: I don't know about the heroin part, but when it comes to places that were used as meth labs, there is a LOT of remediation required to make them safe for occupation.

Tenant shall not be entitled to any other remedy for any delay in providing the premises."

Hypothetically speaking, in Illinois in a situation like this, would a landlord have any rights to the security deposit to remedy the potential vacancy of the apartment til July?

Additionally, the seller must provide a written notice of default that advises the purchaser of:a) the nature of the default, including the amount if the default is a failure to pay;b) the date by which the purchaser must cure the default or the option will be forfeit; and c) the name and address of the seller or the attorney for the seller.The notice of default must be served by hand, sheriff, or certified mail or equivalent.What if the purchaser does not remedy the default?