If the C4 generation is in question; The car has a 4-link (2 on each side from the frame) that holds the hub in place. The cover of the diff is actually a "bat-wing" that bolts to a bracket on each side of the frame. There is also a strut rod from the diff to the rear hub on each side. This ties everything together - the rear end and hubs all form one structural unit. There are no axles, in the traditional sense. There is a stub axle on each side of the diff, held in place with a special C-clip and a short half-shaft to the hub (u-joints on each end) . A picture is worth a 1000 words here..... Point is, the stub axle can't come out of the diff as it is held in place by the half shafts. If the u-joint fails, the stub will be captured by the C-clip.... but who cares, the damage is done with a half-shaft flopping around! In practice, at high speed, the half-shaft will tear itself loose. (by the your chute is out and brakes on!). The wheel will not fall off as it bolts directly to the hub, and the hub is secured at the top by the 2 links, and at the bottom by the strut rod. The hub is capable of standing alone. I've broken a lot of U-joints in other forms of racing, and aside from damage to the bottom of the car from the brief (about the second rotation of the loose halfshaft breaks it free) flopping of the half-shaft, I have been able to safely bring the car to a stop. I emphasise that this example is for a C4 only, because not all IRS set-ups have the hubs secured if the half-shaft.