What is the RS-485 line wire series resistance limitations?
That is an oversimplified model. You should use a lossy transmission line with terminations to properly simulate the circuit. 

In LTSPICE the model is LTRA. Expect it to take a rather long time to run. 

The maximum recommended length is 4000 feet. Assuming AWG 24 wire, that's 200 ohms round-trip. Consider the extremes of common mode voltage and loading (32 unit loads). 



Much more in the NS (now TI) application note [10 Ways to Bulletproof RS-485 Interfaces] (source of the above graph). 

Probably if you are willing to relax the requirements from the standard, reduce data rate and use heavier gauge wire you can use longer wires. You would probably want to go to isolated drivers and/or receivers since it's difficult to guarantee the common-mode voltage over such distances.