Um, the flash get disabled if it's running too hot, doesn't it?
Um, from a Canon flash user guide:
"Do not fire the modeling flash more than 10 consecutive times. If you fire the modeling flash 10 consecutive times, allow the Speedlite to rest for at least 10 min. to avoid overheating and damaging the flash head." Emphasis mine.
The 600 can do around 40 full power pops with a pack in around 2 mins before the screen glows red, the warning sign to slow down, then it locks.