I would seek legal advice sounds like you have to problems 1 the company the other the tenant.
You can go after the tenant not sure about the Management company. http://www.mnhomescontractfordeed.com... more
I can't see why you would be responsible for returning any of the security deposit if they did more damage then the amount of the security deposit -even if the notification wasn't received by the previous tenants within 21 days.
As others have stated, I'm not an attorney but if it were me I would send them a notification in writing now detailing exactly what the damages are and how much it will cost to fix them. I would include copies of any invoices and estimates of repairs demanding immediate payment or that I'll need to take them to small claims court.
Past experience tells me that they most likely won't pay me so I would need to file a claim with conciliation court and let the judge sort everything out.
Check out the Landlord Tenant Rights and Responsibilities information on the Minnesota Attorney General's website.