I've found buried stems of Vanilla tend to rot but just placed on a damp medium and kept moist they readily put out roots. Tops of my old plants often get broken off by falling branches or fronds. The bits on the ground just put out roots and then go searching for something to climb. The old 'beheaded' vines put out a new shoot and head back up. I've probably got 30 or more plants in the garden now from that process. They have more roots on the tree trunks than in the ground. Vanilla is very easy with the right warmth and humidity, some people over think it and end up killing them with kindness.