Why didn't Regulus at least find out how to destroy horcruxes before he killed himself in the cave?

Why also didn't he just decide to live long enough to see the locket be destroyed?

If he believed there was only one horcrux, why couldn't he have drank the potion, see the horcrux be destroyed and then with him believing that Voldemort was Mortal now, try and bump him off?

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