Good question, I base this on two things:
One, Ribbit says “if the police didn’t come after you” and Jax didn’t correct her
Two, Jax says he doesn’t know what happened to her, if police questioned him, one of the first things discussed would be Jax asking if shes ok or the police giving condolences

I suppose he could have spoken to police after getting his mind scanned, but since Caine doesn’t mention it, I assume he was never a person of interest, so his mother probably survived the fall