Nec diū superfuit fīliō pater—The father did not long survive the son.
What kind of ablative is fīliō? I don’t see an ablative of time after which, or something similar, in any of my grammar books.
I’m basically a beginner, so take this cum grano salis, but I believe in this case (no pun intended) it’s the dative, not the ablative, and is the object of superesse. Look up “dative with compound verbs” for an explanation better than I can give.
fīliō is dative. Many compound verbs take a dative complement.
Allen & Greenough sec. 370:
http://www.perseus.tufts.edu/hopper/text?doc=AG+370&fromdoc=Perseus%3Atext%3A1999.04.0001