Just because it's a "type of failure has not occurred on a GE90-94B engine" doesn't mean it's totally unprecedented on other engine models. Thus it probably has been taken into account in ETOPS planning & analysis.
And it MAY NOT even be the engine's fault - possible maintenance error (wrong type of bolt, etc.), torque wrench out of calibration, etc. (I'm only speculating here, but these types of things have bitten many engines in the past.)