Eviction if I owner occupy

[Desalina G.]

Hi experts...

I'm looking at a 3 unit in Chicago with a tenant that, according to the seller, refuses to leave.  I looked and can see the tenant has a long history in small claims court and at least one other eviction.  Seller is saying he doesn't want to deal and buyer has to take possession with tenant.  I assume cash for keys has already been attempted. 

My question is...what's the worst case here?  We are looking to owner occupy.  Does that change anything about the eviction process?  

I spoke to an attorney who said to assume worst case 12-18 months of no payment while we wait to evict.  Also, any damages to the property would be an issue.  

Anything else to add as we decide whether or not to pursue this property?  What should we consider?

In terms of price...how would you "discount" the market value of the property?  My attorney said lost rent * 18 months * any assumed damages.... we could be talking 50K - 60K plus time and stress.  How much would you discount your offer?  

Thank you!