Dumbledore says before he and Harry set off to the cave, that they are setting off to find and destroy one of Voldemort’s Horcruxes, yet when they get to the cave, they don’t seem to think about, or know how they are going to destroy the horcrux that they thought they were going to recover. When Dumbledore is about to drink the potion, he doesn’t know what the effects on him are going to be; he could be paralysed, forced to forget why he was there. He tells Harry to force the potion down him but he gives no instructions on what to do afterwards when the Horcrux is now accessible and Dumbledore is affected in whatever way by the potion. You would have expected him to perhaps tell him to destroy it (presumably with Godric Gryffindor's sword that Dumbledore brought with him, did he actually bring it?) and maybe bring back the incapacitated Dumbledore to Hogwarts. To me they did not plan well, so what were they out there to do, merely find the horcrux or find it and destroy it? Now offcourse, what happens is that Dumbledore merely hallucinates, becomes weakened and thirsty so they just about managed to get away with the fake horcrux, but had the potion made Dumbledore forget everything for example; Harry would not know what to do.
And that makes me think about Regulus Black’s horcrux hunt. He knew a lot less about horcruxes than Dumbledore, but he did know that he was going to die (he told kreacher to leave him to die in the cave), but he seems to have also poorly planned his hunt. It can be assumed that he did not tell Kreacher, nor even find out how to destroy them (he didn’t even tell Kreacher that it was a horcrux, did he?)
What do you think?