Almost all Land Rovers use the same basic hub design with two large taper roller bearings pressed into a cast hub, and bearing adjustment via twin locking nuts with a fold-over tab washer between them. (Don't even think about re-using the tab washer - always replace it.)  Depending on the age and model, the bearings may either be lubricated by the oil in the axle, or else packed with bearing grease.

Good quality wheel bearings will last a long time, cheap Far Eastern ones tend to be made of softer metal and have a much shorter life. Symptoms of impending failure are excess play in the hub (jack the vehicle up and try to 'rock' the wheel on the axle), and roughness/noise when the wheel is rotated.  Lubrication failure is very common on later vehicles with grease-packed bearings (the grease hardens with age) and also on the front axle of older vehicles, where all the oil runs out of the front swivels due to damaged chrome swivels and seals, leaving the bearing running dry.  The same problem can occur where the oil in the swivels has been replaced with semi-fluid grease - that stuff is great for curing leaks, absolutely useless for keeping the wheel bearings lubricated.  If you fill your front swivels with semi-fluid grease, you MUST strip the front hubs and pack the wheel bearings with bearing grease.

If a wheel bearing fails it will probably overheat and break up.  The inner races weld themselves to the stub axle (making the hub almost impossible to remove) and in the worst case the stub axle itself may shear, allowing the wheel and hub to fall off.  Best to sort out your bearings before they get to that stage.