If you had the power to raise the dead...

[Sammy]

But Bach did not write no operas because he died too young! He was apparently not interested in the genre and had so many other duties. Whatever the reasons, I do not think a Bach living 10 years longer in good health would have composed an opera.

You way of looking at this is contrary to the OP.  What's realistic doesn't count here; we are raising the dead!

[prémont]

Never heard of the Commotio,

What a pity - this is a great Work.

[Christo]

If Gershwin had lived more of the full span of the American century, he could have had an unimaginable impact on our culture...

Absolutely.

[Ken B]

I for one wish Debussy hadn't died before he wrote La Mer.

[ZauberdrachenNr.7]

I for one wish Debussy hadn't died before he wrote La Mer.

Buried at sea?  OMG, just when you thought it couldn't get any worse...

[DaveF]

Never heard of the Commotio,

Apparently on the title-page of Commotio, Nielsen wrote "no.1" and then erased or scored it out, although it remains visible.  You can probably see it in the complete Nielsen edition at Det Kongelige Bibliotek's website - I can't confirm as I'm working on an ancient laptop while my PC's Blue Screen of Death is fixed.

but the other wind concerti really are a  great loss (especially because there are not many good concerti for bassoon or horn, after Mozart).

Nor oboe, indeed.

[Madiel]

I can think of at least a couple of other cases of composers labelling something "no.1" only to never write "no.2". I wouldn't put much store in it as evidence that was actually a 2nd piece in progress.

[PerfectWagnerite]

I can think of at least a couple of other cases of composers labelling something "no.1" only to never write "no.2". I wouldn't put much store in it as evidence that was actually a 2nd piece in progress.

As in History of the World - Part 1 ?

[starrynight]

You have a point. Not sure about Beethoven influencing an older Mozart but even the real Mozart dead in 1791 undoubtedly was a towering figure for Beethoven and he did not stop Beethoven becoming Beethoven.

But I think Mozart could and probably would have become even more important for German language opera had he lived longer, certainly for Weber and probably Schubert as well.

Mozart would have done more choral music and Beethoven probably the same amount or more of chamber music.  Mozart in the 1790s could have done more symphonies though, Haydn had recommended that he go and replace him in London I think.  I'm not sure if Mozart would have travelled but he would have probably had more symphony commissions anyway.