I've thought of this often, because I watch both sports.
The formula I came up with is 1 basket in basketball (ie: 1-3 points) == 1 goal in hockey, and then each 7 additional points on top of that is another goal. So it would be:
1 pt = 1 goal
8 pts = 2 goals
15 pts = 3 goals
22 pts = 4 goals
29 pts = 5 goals
And so on. When the US Dream Team beat Angola in 1992 by a score of 116-48, that was the equivalent of Canada beating a scrub hockey country 11-1 (which has happened on occasion).
To answer the OP's question: A 20 point lead in basketball is equivalent to a 3 goal lead in hockey, but a 22 point lead in basketball is equivalent to a 4 goal lead. So it's close to being almost insurmountable, but miracle comebacks have happened.
The infamous Miracle on Manchester in 1982, where the LA Kings came back from down 5-0 to beat Gretzky's Oilers 6-5 in OT, with all 5 goals coming in the third period, would be like an NBA team coming back from a 30 point deficit in the 4th quarter -- just an insane run, everyone hitting their groove at once, maybe one guy nailing like 6 threes in a row, their opponents use all their TOs to cool them off but nothing works, and they tie the game on the last basket to send it to OT, and then win it in OT by one or two baskets.
I mean that's incredibly improbable. But it is possible.