But I wouldn't wait around for the bottom to fall out. It was nice your landlord told you this though. Often people are just served with sheriff notice and evicted because of foreclosure.
When the new owner takes over, they are bound by the lease that you have. If you are month to month, the new landlord has to give you a 30 day notice that your lease will be terminated. If you got a 30 day notice today, you would have to be out by September 1st (assuming that your rent is due on the first of each month.
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However, there's a complication. You say the landlord told you not to pay rent. That's fine for you right now. (However--and because I'm not a lawyer, this isn't legal advice--I sure hope you got that in writing.) However, the current owner may be setting you up for an eviction. You're violating the terms of your lease--unless your lease was modified to require $0 monthly rental payments--and thus helping build a case for your own eviction. I don't know how the landlord-tenant courts in Cook County operate--whether they're friendly to tenants or to owners--so I don't know how long it'd take to evict you. It could be just a month; it could be close to a year or more.
Again, I'm not a lawyer, so this isn't legal advice. But at the very least, for your protection, you should have something in writing from the landlord regarding non-payment of rent. Ideally, execute an addendum to your lease reflecting a rent of $0--or probably something close to it, like $25 a month. Again, run that by a lawyer.
Hope that helps.