Leather Restoration on MOD 'Culloden' Brass Cantle Sporran

[Alisdair]

As a leathercrafter, I have to say that the subject of restoration is a delicate one, as any restoration carries some inherent risk. If the leather object is precious to you, you don't want to risk any damage, so you don't restore: you stabilize and preserve from any further degradation. There are specialists in this domain.
On the other hand, if the risk of damaging the object is an acceptable one, restoration of a bag in this state is not necessarily an expensive process. You could consider: restoring the shape of the bag (this one has a bit of an assymetrical sag), fixing any broken stitches/tears, reconditioning the leather (it's probably a bit dry or brittle), recolouring it (a pity in my opinion, as a patina is a unique thing) and refinishing it (a nice wax coat). If some parts are too thin or saggy, I'd attempt applying some backing (canvas or leather) on the inside of the bacg, which would make it firmer.
...the process to deal with some of these issues will vary according to the type of leather used (vegetable tanned vs chrome tanned, for example)