FOAK: One way flights (and Mexico)

We leave Canada in mid-April to return to <location still to be
defined> in the UK. As part of the return package, I can take the cost
of the business class fare to the UK (for a family of 4) and arrange my
own journey within that limit, with pretty much no restriction on the
route.

I quite fancied going the long way round with a round the world air
pass and travelling west, but SWMBO is not at all keen on the number of
flights involved.

So, the compromise has been that we fly to San Francisco and do some
touring in California and Mexico. All well and good, but when I looked
at flights it appears that a one-way ticket is around twice the price
of a return, which seems a bit odd and in defiance of logic. The
question is, for the seasoned travellers, if we were to simply buy a
return ticket and discard the return leg, would we face any potential
difficulty? Personally, I can't see Richard Branson getting on my case
but is there any sort of contractual commitment to fly both ways?

Any recommendations as to which part of Mexico would be better, bearing
in mind the two sprogs are only 3 and 8? Realistically, I would expect
either coast of the Gulf of California would be the most achievable,
but which side?

cheers,

 

I would recommend the West coast on the "mainland"[1] around
Mazatlan or Puerta Vallarta and try & visit the Copper Canyon.
However, with young children Cancun might be a better bet.

i.e. not the Baja California penunsula