I believe that if the Dark Ages would never have happened, then we'd have a huge jump in modern technology and possibly be able to colonise other planets, as the Dark Ages left Christian nations at a huge loss behind the Byzantines and Muslims in the East.
If the Dark Ages wouldn't have happened, however, there is a good chance a fair few of the modern religions we have today may have been eradicated.
I disagree with this assessment. Rome was stagnant and I see no reason to think that a Western Empire that survived would have behaved any differently than the East. Byzantium (a Christian nation, by the way) wasn't hurtling toward the space age, so I don't see any reason to think the West would have, either. The Dark Ages were overstated by 19th century historians, in any case.