I don't think you are going to get many responses from people who have put over 100,000 miles on their C50s- there are only a few owners on this site with that many miles on their bikes, and they have all replaced their entire engines at least one time, sometimes multiple times.
You are going to get a lot of responses with cam chain problems in the 40,000-50,000 mile range. Myself included- cam chains starting to have problems with 45,200 on my meticulously maintained 2006.
The C50 is an inexpensive bike, with a very small engine for a bike as physically large as it is, and steeply geared to make it work- my C50 is actually slightly longer than my Electra Glide, but the Harley has an engine more than twice as large. So it stands to reason that the bike with the 800cc engine that cost $6,699 brand new is simply not going to last as long as the $18,999 bike with the 1700cc engine and six speed overdrive transmission. Cars are the same way- no one would expect a $11,000 Chevy Aveo to last as long as a $35,000 Acura RDX.
A C50 should give you 40,000-50,000 good miles. As the average owner of a small Japanese cruiser only puts 3,000-5,000 miles a year on their bike, this is considered to be a more than acceptable life span, and is about what you would get out of similarly priced and sized models. If you want a bike that will last 100,000 trouble-free miles, get something much larger, like a Kawasaki 1500, a Honda Goldwing, a Kawasaki Concours, anything from BMW, or anything from Harley that is not a Sportster.