What drives India into Asia beneath Tibet?

Answer: Three mantle currents meeting in one spot

Three mantle currents meeting in one spot ✓ — Correct! Beneath Tibet, three hemisphere-scale mantle currents converge — one from the Pacific, one from Eurasia, and a fast-moving flow rising from beneath the Indian Ocean. Their meeting point is what keeps pulling India northward into Asia. The Indian-Ocean branch is the most aggressive of the three; it's the real engine of the collision.

A magma pool keeping the crust afloat — Not quite. Tibet sits on the thickest continental crust on Earth, but that crust isn't floating on magma. It's solid rock, thickened by compression. If a magma pool were actually there, you'd get a giant flood-basalt province, not a plateau.

Old seafloor slabs locked in a stalemate — Not quite. Subducted slabs do sit beneath the region — you can image them with seismic tomography — but they're sinking, not locked in place. What drives the collision is the mantle flow converging above and around those slabs.