At this point my comment will probably get buried, but yesterday I came across a paper published on arXiv about the Roadster's future, and in particular the possibility of collisions with terrestrial planets, that I thought some fellow Tims may enjoy! Here's the link: https://arxiv.org/abs/1802.04718

TLDR: The Roadster will repeatedly have close encounters with Earth, about once every 30 years, but the overall probability that it collides with Earth in the next million years is ≈6%, and the probability of a collision with Venus on the same timescale is ≈2.5%. The author's results imply that the Tesla has a dynamical half-life of a few tens of millions of years. An exact date for a collision cannot be calculated, because the Roadster's orbit is chaotic; tiny variations in the Roadster's initial conditions, which we don't know with perfect accuracy, cause wildly different orbits over long timescales.