It depends on the film type.
Overexposure builds density in color negative film and at least up until you reach the Dmax of the film you can continue extracting detail. The shadows correspond to lower density on the negative and it's quite literally impossible to resolve detail if density goes to base+fog(Dmin) as there's no detail there.
Some of the best color negative films like Porta 160 can have 10-12 stops of dynamic range between Dmin and Dmax. Even 10 years ago, that was better than a lot of digital cameras.
Reversal film(AKA Slide Film) is the opposite. Highlights are base+fog(Dmin) and shadows go toward Dmax. You CAN extract detail out of the shadows to some extent, although it tends to need a really good scanner(sometimes you need to do multipass scanning, which presents its own problems) and the overall dynamic range is typically in the 4-6 stop range depending on the film.
One key difference with film, though, is that the falloff at extremes of exposure tends to be gentle whereas digital, especially older cameras, would chop the highlights rather sharply. That could be really ugly when the channels clipped at slightly different levels and you'd get color fringing. I think the worst camera for that I've used was the Nikon D2H, which used a Nikon-developed sensor called LBCAST that was awful and was only used in that camera. The CCDs used in other early Nikons could have that trouble also. I've been meaning to start a thread here on using early digital cameras, as in a perverse sort of way I enjoy using my D1 series cameras and seeing how far we've come.
