Sooo, isn't basilisk venom something that destroys Horcruxes?
Aren't giant snakes Orochimaru's favorite thing ever?
Doesn't Orochimaru have access to, through Ryuchi Cave, a vast number of snakes, many of whom likely have special venom, like Garaga's petrifying spit venom? He could easily find a basilisk himself, if an equivalent doesn't already exist within Ryuchi Cave, and put a Summoning Contract on it. And then he has mobile Horcrux destroyer. Orochimaru is definitely intelligent enough to read through Voldemort's movements; and honestly, the way the Ministry of Magic is written, they're hilariously incompetent at their jobs.
I'd argue Orochimaru is a good deal smarter than either Voldemort or Dumbledore, honestly. Orochimaru was not only a master with manipulating chakra and jutsu on a level equalling or possibly surpassing Dumbledore and Voldemort's genius with magic, but he was well-versed in science, which is something neither Dumbledore nor Voldemort seem to give any weight to. Given the fact that the Unforgivable Curses can be blocked with simple inanimate objects, something that Orochimaru would no doubt be aware. The Rashoman gates, Earth Release: Mud Wall, Hiding Like a Mole/Hiding in Surfaces technique to phase through the ground, shedding his skin to misdirect Voldemort's spells when the real one has escaped underground...
I really don't see why anyone thinks Orochimaru doesn't take this, adding in his enormous AP advantage.