...seem to have enjoyed using the
lawn as a toilet as there are many bare patches on the lawn at the moment

it may not be the dog and cats - in my experience cat urine does not kill
grass, and I think that dog urine (as opposed to bitch urine) doesn't
either. It may be leatherjackets (baby crane flies) causing the problem. As
the previous poster said you could just leave it, alternatively just scrap
back the dead grass from the patched and sprinkle on some general purpose
grass seed mixed with compost but wait for a few weeks first till it starts
to grow properly.

Hayley
(gardening on well drained, alkaline clay in Somerset)