I must admit to being a bit of a hypocrite about this topic. In theory, of course any bits of my body or my loved-ones bodies which can be used should be used. But ... but ... when it comes to my children (adults now, but you know what I mean), I would find it incredibly difficult to consent. I once heard someone say "I want them to return as intact as they came." That's how I feel. I know ... I know ... that isn't logical, isn't rational and, given that I don't even believe in an afterlife, isn't even understandable. However, that's how I feel.
Having said that, as my 'children' are now fast approaching 40 and are well able to make their own decisions, and both agree with presumed consent, I hope I would be brave enough to agree should that awful day ever come.
I would feel differently if asked for consent in my husband's case though. I guess it's having given birth to them which makes the difference and that they will always be my 'children.' He is someone else's 'child,' so it's ok.
(I am aware that this is a bit of a stream of consciousness reply. I've tried to make less so, but given the subject matter, please be understanding.)