There is not much information about when they will first contact him, if he wants PR then he will most likely use his child as the reason he should still be granted the visa.
Again there is not much info on how they will deal with his reasons to stay or how long they take to process that claim.
Should they refuse his claims and refuse his PR visa, he can and most likely will appeal the decision at the MRT - there are some wait times for these hearing types but I don't know them only they will be getting longer due staff levels.
It seems most cases that he will likely be granted PR due being biological father, if you feel the need apply for a protection order.
** I think I asked but did not get a reply - What reasons did you give immigration for withdrawing sponsorship?