that should be not too bad then. but take note of the balance between the background and subjects in the foreground, especially when the background is far from the subjects.
If the flash lights up the subjects in the foreground properly, it'll not be sufficient to light up the background (and it'll probably cast an ugly shadow). If the flash properly exposed the background, the subjects in the foreground will be overexposed.
You might need to tilt the flash (and/or use a bounce card) and adjust the shutter speed (a faster shutter speed means a darker background, while a slower one gives a brighter background) to achieve the effect you want.