Basil only blinded (counting the ones left with one eye) 14 or 15 thousand. Only part of Samuel's army. And after finishing conquering Bulgaria, he governed it with a light hand.
Anyway, let's say Basil has a son. Let's say his son is thirty or so when the old man bumps off.
Great, the Macedonian dynasty isn't dependent on an old pleasure lover and his mostly useless daughters.
But Basil having a son doesn't necessarily help matters. His son might as easily be - and I'd wager is more likely to be - an Edward II to Basil's Edward Longshanks than a man in his father's mold, especially as Basil seems like the sort that would be very, very, very hesitant to trust his son anymore than anyone else with any power or responsibility.