I got it the year after I became a teacher so fall of 1997. The bag has been slung over my shoulder for at least 185 days for 18 years - many years serving with me when I had two jobs. Today I grabbed it and the side just split open from all the wear.
Aaahh. So satisfying when a good bag gets used all the way to the end. But yes, if it was a side seam that split, I bet it’s worth looking into repair. If it’s a worn spot in the middle, hmm, I wonder if the panel is replaceable?
Unless, of course, you’re looking forward to new bag shopping. Good time of year to do it. I suggest luggage stores.
For something that doesn’t really need an accurate fit, you can trim off the torn original seam line in the leather and sew it back together for a net loss of 1/2" or so.
Or someone into Living History or black-powder shooting. I would seriously consider holding on to it and running it past someone for possible repair.
I still have and use the American Tourister briefcase I got in college back in 1975 so I share your pain. Don’t know how I will react when it finally dies.