lets say they redid FO1 and 2 and made it one game with the engine of fallout 3
had the same quest and everything
would it crash and burn?

I think so (that it would crash and burn)

This has been suggested plenty of times in here, and always gets a lukewarm at best reception. There's no need for it as the originals are still playable, it would take an A-Grade budget but not be able to get an A-Grade price, and well Metroid Zero Mission showed us its just not a good idea to go back.

Lets create new stories.

The sheer amount of dialogue would pose a serious problem, because a vast majority of NPCs from Fallout and Fallout 2 have fully realized dialogue trees with multiple options depending on your own choices.

To say nothing of the fact Fallout and Fallout 2 wouldn't work in a Fallout 3 engine environment because neither game have realized Wasteland components. You have towns, and some encounter grids. Ever just stopped on a map grid and gone local? A whole lot of nothing, that's what you see.