Growing a Cherry Tree- From seed or to graft?

I recently bought a property that came with a dozen established fruit trees; one of them is a massive sweet cherry that produces the most delicious cherries (Which is hard to pull off in the climate I live in). The cherry tree is almost 20 ft tall so I don't think it's been grafted (original root stock). I'm not sure if its because it age, a fungal infection, or years of neglect but it's been dying off quite quickly during the summer despite being irrigated. I plant to heavily prune it back but I'm not sure its going to make it. I would love to keep this genetic line but I'm not sure the best way to go about it. Should I try and propagate them from seed? Or graft some branches on to some other already established trees?

I would be inclined to try both methods.  Grafting will insure the same cloned fruit so you know you will be happy, but by seed, you might be happy too with the fruit, if not, you can cut it down.

Edit: or if you do not like the cherries on your new cherry tree from seed you can always graft on to it in the future.