Take another look at the original sentence:
You wanted to fix it this way:
To delete the comma between buns and Bo would cause an equally bad problem, a fused sentence. A fused sentence occurs when you have two main clauses joined with no punctuation whatsoever. He had money only for hot dogs and buns is the first main clause. Bo was pretty sure is the second main clause. The spot between buns and Bo needs a stronger break than blank space.
You might want to consult the rules for fixing comma splices and fused sentences.