with a kit the fame will crack anywhere between, 15,000 and 20,000 miles.
if its rigid w/o a brace, the frame will crack anywhere between 2,000 and 7,000.
a cracked fram is usually the sign of a bike that must be retired, i welded my frame back up once on my rigid moby but it started leaking again several months later then i got nailed by a car and it was kaput.
all the other parts around the frame will break down usually b4 the frame especially on kitted bikes, but that's just regular maintenance, and if u have a magnum frame that cracks it doesn't effect the gas tank so it can be fixed easily essentially forever.