Many things can happen due to too high RPM. High centrifugal forces, high loads on the bearings together with insufficient cooling via the oil flow, maybe as well aerodynamic problems on the blades.
I have heard of two incidents, one to a DC-9 of OS and another one to a Tu-134 of Interflug, where one turbine shaft broke and the turbine was briefly running without any load. They rapidly spun up to above 100.000rpm; the bearings did not like this and the wheels soon departed the engine casings. In the case of the OS plane the parts seemingly crossed the rear fuselage and narrowly missed the other engine. Unfortunately, I cannot find details on those occurences on the web.