I don't think they would have stood the test of time.
I saw them in Chicago, in late-1973, early-74, opening for Steely Dan. They were amazing. I hadn't really been a fan until then.
I worked at O'Hare Airport and very early one morning, before dawn, I was on my way to work, near the airport, and the radio station I was listening to played 3 Jim Croce songs in a row. That was unheard of then, on an AM station. I drove under an overpass for planes, just as the dj announced Jim Croce had died in a plane accident, like my hero, Buddy Holly. Gave me goosebumps!
He was very good at what he did, I certainly enjoyed him in concert, but I can't imagine what else he could have done! Steely Dan, on the other hand--Wow!
They probably would not still be a duo, but would get together from time to time. Jim would have been 70 this year and every living, notable singer/songwriter from that era is still performing - so without a doubt Jim would still be playing and singing. He was such an extraordinary talent that he would also have written books, hosted tv shows and been in many movies.
Did someone actually post here that Croce would not have stood the test of time? Are you serious? He was quickly becoming the yardstick by which singer/songwriters were to be judged. Not only that, but he would have created new boundaries in songwriting and performing and he would have stood the test of time on those as well.
Croce was great but he was still alive he'd be in his late 80's. Most people retire by then.
I think they would have run a longer course. Several others of a similar variety from the period did well for awhile, but times and tastes change. Remember how any performer who could sported the Jesus look, but by 1983, those guys were nowhere to be seen. None of them.
I would still be Listening. He is my All Time Favorite. :)