Jon, Jon, that's exactly what I'm considering. First, I asked BiggerPockets fellow Landlords community for suggestions, then I've been researching local and State laws and regulations. Turns out that Landlords in the State of IL are NOT the only ones who are responsible fot honoring the lease agreement, according to Illinois Attorney General and other sources. In fact, other sources suggest that there are ONLY certain categories (at least in the State of Illinois) who have legal reasons to break the lease and are exempt from liability to follow through with their commitment as far as honoring the lease and NOT incur any penalties at the same time:
1) active members of the military, who must change their station;
2) the lease itself being illegal contact (ours was prepared by a Real Estate Attorney, so we are actually in great shape as far as that goes, and we own our property, therefore, have full legal right to rent it out, and full reconstruction was performed up to all existing codes, with all required permits - these are conditions our mentioned above tenants moved in - to EVERYTHING BRAND NEW! and now want to leave..).
3) if a tenant was a victim of domestic violence within the past 3 - 6 months.
4) if Landlord has not maintained the premises in a fit habitable manner (we are so far from that, so much we've spent time or attending their concerns, improving the property and repairing and replacing whatever broke, still wondering if it was a result of tenant's neglect.
5) if Landlord has breached the rental contract
Since none of these scenarios apply to us and our tenants, they do not have sufficient reason to break the lease and not incur penalties, but to leave us with damages to mitigate.
https://www.moving.com/tips/4-potential-consequences-of-breaking-a-lease
Illinois State Bar Association states that written leases prohibit the tenant from subletting the premises, and such prohibition IS enforceable by the law.
It also states that the security deposit is money deemed as a security for any damages to the premises or non-payment of rent, and is to be returned to a tenant if no damage has been done beyond normal wear and tear.
Illinois Attorney General also states the security deposit is to be returned within 45 days after move out date, if: building/complex consists of 5 or more units, tenant does not owe any back rent, and cleaned the premises themselves before they moved.
Hope this information will help other Landlords in our area should run in to a similar situation as we did.
At the end of the day, I have faith in our tenants still, and realistically, despite negative predictions, it will take months before the closing will take place on a purchase of their own house. And before we know it, it will make no sense for them to break the lease when it will be close to their lease end. But I'll be prepared to advertise our property to re-rent as soon as I receive a written 60 days notice from them.
Thank you for your advice! We really appreciate it :)