If it's broken, it's broken. Taking the boot off isn't going to break it any further, since they're designed to be removable, so no reason not to. When you take it off, check to see if any plastic bits fall out.
That's generally the process I was referring to, though I'd advocate slicing the boot open at the sole, rather than rolling down the boot. Rolling the rubber might stretch and distort it permanently.
Doing so would also make it easier to dremel out any remaining plastic in the way of where your replacement foot tube is going to go, as well as make it easier to make sure you have a secure connection with the glue.
Yeah, it doesn't take too long, but if this is the guy's first time doing such a repair, I'd advocate taking your time and doing it slowly, rather than rushing and possibly messing it up.