Sagging top floor of a duplex. Potential deal breaker or not ?

[Mohammad Nur]

I have made an offer to buy a duplex which was built in 1940s. During the inspection, the inspector pointed out the sagging of the top floor to us. Picture is linked

https://imgur.com/a/w5BhAXs

As you can see that it's quite noticeable. My initial thought is that the added weight of the bathroom, water heater etc. during the renovations made the top floor to sag over the years. There might have been a column at downstairs unit which was removed at some point, we couldn't tell.

So, my question is what would I need to do to remedy this situation ? Should I just back out ? This is my first house and everything else in the house is in okay condition requiring minor fixes. 

Additional info: 

- Sale price of the duplex is 299 K (Seller paying 7 K towards closing)

-Sale 'as is' condition

-Property in an A neighborhood, property condition probably B.

-It currently rents for $ 2450/ month.