If you have a drain stack that the 90 has cracked or worn a hole, then you could get consistent leaking at the point where it changes direction.

You don't have to put square peg's in round holes. 

He secured all four doors with heavy deadbolt storm doors and fixed a hole in the roof. 

I agree with you that this program will be one of many factors in why prices increaseThere are two kinds of inflation:1.Non-monetary inflation.

Who is filling nail holes?  

When you find yourself in a hole, stop digging.

Listening to the wrong people can put you in the hole fast.

If you where going to be able to recreate the orginal layout, you would of been able to do so by the clues left behind by remaining framing, be it the "honey" holes where the toliets once where, the sizes of the holes in the joist would indicate what pipes ran where be it hot and cold supply, toliets, showers and other industry standard tell tale clues. 

They also have strict rules for renters about sharing the kitchen, cleaning, etc. with monetary penalties for not complying. 

Always get monetary concessions... never rely upon a seller to do anything after closing, unless you want it done half-assed and on the cheap.