Thanks @Lumi Ispas, they responded with an offer for $3k, but the attorney was unwilling to add language regarding the condition of the unit, i.e. they won't guarantee there isn't damage beyond normal wear and tear.
Additionally, one thing that's been bothering me, and I'm interested to hear Chicagoans' takes on this, is that technically these tenants have not terminated their lease. The RLTO states:
The tenants sent a notice of intent to vacate 24 hours after they notified me of the power outage. According the RLTO section above, this was too early. Additionally, the language in their letter made no mention of termination of lease, only that they would be leaving the apt on 5/31. They have not sent me any formal termination of the lease, so technically the lease is still active, correct?
If the lease hasn't expired, then what gives them the right to pursue their security deposit? Granted, I did not hold funds in a separate account, but it appears that's a moot point if I return the security deposit in a timely manner with interest. See RLTO section below.
I'm taking "subject to correcting a deficient amount of interest paid" to mean "in the event that the landlord doesn't return the deposit with enough interest".
I think it's easy to pile on and focus on the obvious errors I've made, but it seems the tenants made some errors as well. Also keep in mind that I offered to put tenants up in hotel, pay for groceries, etc. The unit's heating is forced air, so they had heat. By all indications they stayed in the unit, but I was still happy to reimburse them for more than prorated rent because I was appalled at my mistake.
@Brie Schmidt and @Jeff Burdick please poke holes in my RLTO argument, I've been spending too much time on this and wouldn't mind just settling, but I wonder if I can, at the very least, negotiate down further after citing these mistakes to the attorney and the tenants.
Thanks @Ronan M., your earlier post motivated me to do some more homework on this.