The strap is a disposable item
When they are worn I throw them away
If the buckle is worth saving (OEM) I keep it if not it goes in the bin as well.
That said, I tend not to buy watches on leather straps as I don’t like them and all watches seem better ‘value’ when bought with the bracelet.
Re prolonging life other than keeping them clean and maybe a bit of neutral colour leather polish every now and again there is not much you can do.