a flight booking plan - is there a downside to this?

I need a one way long haul flight back to edinburgh in November

all one ways, as u know, are turbo £

if I book a return and just don't use the return leg, how likely is the airline to come and sue me?

Make something up.  I couldn't fly because I was flatulent / hungover / had a cold.  Because I would have been denied boarding due to a typical night out is a plausible one.