I've no expertise to draw on so I'm sure it'll be easy to shoot me down but, to take one example, it doesn't seem inconceivable that the use of EPO or blood doping to increase the ability to get oxygen to the muscles may allow the athlete to challenge and hence develop other parts of the system more easily, like lung capacity or numbers of mitochondria. One would expect those gains to reverse themselves more or less quickly after doping stopped, but I don't know how easy it would be to get funding to find out how quickly for different aspects after stopping different kinds of doping.
Maybe someone with a sports medecine background knows?
Beyond that, surely you'd have to consider the relative benefit of deterence against the value to sport of allowing the possibility of redemption. If there is no possiblity of redemption, then what incentive to come clean? Of course you could reasonably view LA as a special case, and/or his repentance as insincere.
Glad to have got that off my chest. As you were!