'If one parent has died in childbirth, the surviving parent ought to get leave to care for the child.'
No issue here, and inclusive language that makes no assumptions about what configurations of couples/identities you're talking about. There is no possibility that the 'surviving parent' could simultaneously have given birth and died in childbirth, is there?
(Yes, ok, I accept that in theory, two lesbians could go into labour simultaneously. But in that situation, I'm not even sure they could both be recognised as parents of each other's biological child, since HEFA does not allow lesbian couples to do fertility treatment at the same time.)