+1 I don't think the PI has grounds to be annoyed with him for not sticking around when the person he expected to work with isn't going to be there, and as someone who isn't an established member of the lab he might not be so sanguine about hopes of subsequent funding, the other PIs' work less attractive to him or whatever. Post-docs do need to look out for their own careers. But he's being ridiculous in expecting to get early notice of a pregnancy like that, and the PI can quite reasonably be annoyed by his demanding that.