If you Google leather care you'll probably find some info about 'feeding' leather to keep it supple - however, make sure any product or restoration tips are suitable for a camera case - not much point in having a supple but sticky camera case that stains everything it touches!
I've used a product I was given when I bought a leather sofa around 12 years ago (which I think may be lanolin based?). It's applied with a moistened cloth and rubbed into the leather, then the excess is polished off after about 15 mins when it's dried. When treating an old camera case, depending how dry it is, I will typically give it three or four applications over a period of two or three days, paying particular attention to any areas that fold or hinge. Other leather care products are available though, this is what I've used because I already had some!
I also inspect the camera strap and its fixings and buckles for any wear and tear, signs of cracking, splitting, etc. I figure this is probably going to be the main cause of the camera hitting the floor if it fails, so I don't take any chances if it looks suspect or there are definite signs of the leather cracking or tearing at the case anchor points, etc. I have a couple of cases that I'm not using as I don't trust their strength, and one where the strap actually did tear free from the case when pulling the camera off a shelf.
I imagine a qualified and experienced saddler would be able to give you some advice on restoration, leather care and whether or not the case will still be strong enough to do its job. I would think they should be able to replace case straps safely too. After all, they're dealing with things like reins, bridles and stirrup leathers, and if one of those should break then a life could be lost, not just a camera dropped!
However, whether or not the charge for a saddler's time to carry out major repair work, such as making and fitting a new strap to match, or completely refurbing a case, is economically viable will most likely depend on the value of the camera and case, as we can't expect a time-served and skilled craftsperson to work for virtually nothing just because we've bought a £30 camera with a tatty case. Hope this is useful.