What if post! What would have happened if Aragorn was not part of the fellowship?

Short answer: They would have failed. But I can't think of anyone who could have realistically replace him, at least not among Men. Maybe Glorfindel would have been sent with them after all (Tolkien was originally going to have Glorfindel as part of the Fellowship, but replaced him with Legolas).

The presence of a powerful High Elf such as Glorfindel might have proven true Gandalf's concern about drawing too much attention.

Aragorn originally didn't exist, so yes, the Fellowship would have made it with Aragorns original character, a Hobbit named Trotter.

Yeah, but I'm not counting Trotter as he was completely cut out of the story and we don't know how Tolkien would have developed him and the narrative if he had remained.. But speculate away!

What would Aragorn be doing if he weren't part of the Fellowship? It's possible he would lead the Grey Company to Minas Tirith, but he may not have gone through the Path of the Dead, and he wouldn't have had access to the Orthanc Palantir. He wouldn't have formed a strong alliance with the Rohirrim. Without his actions, he may never have become King of the Reunited Kingdom and thus never married Arwen.