I'd be willing to bet that guide failure isn't usually the direct result of chain elongation but however, the failure of the tensioner to take up all the slack.

And, I'll bet even more money that there are sufficient warning signs prior to this failure as well (rough uneven idle, poor performance, excessive noise from the chain vault ect.)

Obviously, the tensioner can't do it all but poor maintenance (infrequent oil changes for one) would allow the oil gallery going to the tensioner to eventually gook-up and not pressurize the tensioner (IIRC oil ony flows into the tensioner cavity, not through it). Ultimately, when the chain had elongated enough for the tensioner to move to the next detent, it wouldn't/couldn't and voilá: chain slap, slack and eventually whap, there goes the leading edge of the guide just downwind of the cam sprocket.

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