(b) Baez has written elsewhere that he's risk averse with respect to charity. Thus, he may reject expected value theory based utilitarianism.

You can work towards a positive Singularity based on purely selfish motives. If he doesn't want to die and if he believes that the chance that a negative Singularity might kill him is higher than that climate change will kill him then he should try to mitigate that risk whether he rejects any form of utilitarianism or not.