If the flight number changes, such as in your example of 9W 119 and 9W 76, they're different flights (in fact, nearly always different planes) and you'll have to disembark. Technically this is not a stopover at all, it's a transfer or "layover".
If the flight number stays the same, you've got a genuine stopover, and there's no easy way to know what will happen. If the stop's an hour or more, usually you will have to disembark while they clean the plane. Being allowed to choose to stay on board in these paranoid days seems to be getting more and more unusual, although it does still happen on some regional hopper routes where stops are short (under an hour) and only a few pax may get on or off at any given airport.
Not being allowed off the plane at all is even more unusual, and is mostly limited to stopovers at military airports (eg. Kwajalein on the Continental "Island Hopper" between Guam and Hawaii), domestic legs without cabotage rights feeding international flights, or those rare routes where they do a pure refueling (technical) stop. The last of these are increasingly rare in scheduled aviation, but do still happen on crappy charters flying (eg.) Scandinavia-Thailand on old overloaded planes that can't fly the full distance in one hop, or even on scheduled flights if there are last-minute equipment substitutions, really bad head winds etc.