Positive  PCR result after covid recovery. How to travel? If someone  gets covid, recovers but has to do a PCR test and fails due to 'traces' how do they return  home?

You don't. You quarantine until you test negative. 

Emirates will take you after 14 days from the first positive. 
good to have also antibody test/s pin&p.rick and from syringe blood. 
even if private they are $50-100. 

at dubai can do airside pcr for $50, waiting time 20 minutes. Located right between terminal b and c. Possible also at terminal 1. 
 

at BKK they might do antibody for 3k and release after doctor's consultation. 
local authorities might order to selfisolate

Where are you coming from and where are you going to ?

 

Have a look at this topic . . . .

 

How to return to Thailand with COVID recovery certificate on Page 2