in FONV I would have to say its possible. You can get pulse slugs that deal an EM damage to targets, you can get dragon breath shells that deals damage as well as light your targets on fire. You can even get traditional magnum, slug, and buck shot.
In FO3 I would say it would be very hard considering they use basic shotgun shells and there are some enemies that are very tough that I dont think a shotgun would take down. The Ghoul reaver for instance is one of the hard enemies that is a bullet sponge and I dont think I never took one down with a shotgun.
On roleplaying, I would have to say I do that, every time I play these games I always put myself in the situation and how I would respond in real life. Then there are those times where I deside to be a complete jerk and become a grimreaper killing anyone who tried to get in my way.