I get your point but to me its kind of futile to ague about it on the basis of story realism .That's a bit of a stretch and a long con if it was the case then Neil might have done it to protect the MC but no I'd say she's dead it's just too much a revelation like that would break the MC and one thing I wouldn't want to see is some drama between Neil and the MC we got enough going on without that. Plus Neil seems like a stand-up guy and has gone out of his way to provide what he can for his son.
DPC is creative enough to design a scenario to fit the narrative smoothly and drop a bukkake of drama on it
but he hasn't done it ....not just mother even sisters,aunts and grandmas are absents....is both of his games..why?
I think its Simply to keep the "motherfuckers" out
once he introduces any attractive female relative the huge incest crowd would flock around asking for the forbidden and he might have to make tough choices to disappoint people
killing the mother at the start was psycopathic but clever move by dpc to avoid these situations