I'm not shure, but I've heard around 10,000 rnds. Then the throat becomes worn, and accuracy drops, then a new barrel will rezero the counter. The other things which are more likely to drop accuracy is a copper build up in the bore, or a damaged or worn crown by improper cleaning. The way to get the most out of the barrel is to clean with a good copper cleaner (go by the cleaners instructions as some are harsh, and can damage the barrel if not used per instructions). I use Hoppe's BenchRest Copper solvent.
Use a bore guide if you use a cleaning rod, or use a TAC-Jag or cable to clean so as not to wear out the crown. Lube the bolt, and slide rod guide slots in he receiver with a gun grease or Dri-Lube teflon, to prevent excessive wear. Finally keep the barrel heat down. The excessive heat will accellerate barrel, and throat wear. Under normal use the mini should last a long time, maybe even a lifetime. Now if you shoot 30 rds every day for 1 year. It will last 1 year. Many BenchResters buy a new barrel each year, as they shoot a bunch.