Can the Avatar still be reincarnated?
Actual Avatar reincarnation means Raava accepts part of current Avatar soul, leaves its body, and finds new Avatar. Communication with previous Avatar incarnations was exactly communication with parts of their souls inside Raava. Since Raava got itself destroyed, and then resurrected, it is in "clear" state, without souls of previous incarnations.

But while Raava exists in this world, it can find new vessel to become next Avatar incarnation. The only consequence of its temporary destruction is that Korra is now much like Wan.