What if Roman hadn't colapsed?
We'd be a 1000's years ahead?
If it hadn't been for various collapses of assorted Western civilizations alone there wouldn't have been the opportunities for a lot of advancements we take for granted today.
For example, if the Greeks hadn't self-destructed with their Peloponnesian War, the Macedonians (rude, country barbarians to the rest of the Greeks) may not have been able to rise to power and spread Hellenism throughout the known world at the time.
If Rome hadn't collapsed when it had, maybe they could have reached a greater cultural rapport and bond with Constantinople and formed a larger empire by supporting one another. If either had made better use of the sea for trade that alone might have been something else to keep Rome going longer.
Who knows? I don't know that we'd be 1000 years ahead of where we are now, but it would be a very different world. If the Dark Ages hadn't happened after the collapse of Rome, and the Renaissance hadn't flourished in Italy, but died in a worse pandemic than happened, what would have happened then? The northern Renaissance was hardly the scientific bloom it was in Italy, so maybe that would have stalled advances made by a more scientific age. Not that Rome was all that scientific, though they were awfully good engineers.
And mind you - none of this takes into account how China, Korea, India, or even Japan might have filled the vacuum left by the Western empires. Jeez - if Constantinople hadn't firmly established Christianity in Eastern Europe would the Turks had an easier time advancing west and/or actually made it to Europe and kept a lot of it? So many what if's, so little time.