He probably refers to the Operation Deliberate Force that finally persuaded Serbs to accept the deal that was on the table.
Well without that intervention, there would eventually be a cease fire. All sides were getting exhausted by the fighting.
However, without any foreign intervention whatsoever - ie no-fly zone, humanitarian aid, sanctions against Serbia and all that, it is hard to see anything other than eventual Serbian victory, at least in short to mid term. It would create a massive humanitarian disaster as many people would flee the country. The end result would probably be Bosnia divided between Croatia and Serbia. A few tens of thousand people more would probably be killed by the Serbs in Eastern Bosnia like in Gorazde, but that is about it. There certainly won't be massive slaughter of Bosnian Muslims, whose core areas (Tuzla, Zenica, Bihac and parts of Sarajevo) would probably be part of Croatia. Sarajevo would be a divided city.