LotR -- Book 5 - Chapter 04 - The Siege of Gondor

[Kuruharan]

Ok, but there would have been no Aragorn-Arwen marriage, with the loss of that bloodline stretching back to Melian & beyond.

Well, yes this is true. This is an almost "elvish" point in not wanting this last little bit of "magic" to pass from Middle-earth.

If the king had not returned it would not have made such a grand ending (in such case some "modernist" critics might have found it more appealing). However, Gandalf as a character could not concern himself with such things. On the other hand, he was rather "elvish" in disposition.

Maybe the people of Gondor would have adopted a new system. If Aragorn had died, leaving no heir, then there would have been no one else to rule. Faramir was a beloved leader in Minas Tirith, and perhaps knowing that there was no "rightful" king anymore, the people there would have decided to Faramir instead. Kind of like how in the youth of the US, people wanted Washington to be king.

I think Faramir would have had a reaction similar to that of Washington.