We present Chandra and VLA observations of GW170817 at ~521-743 days post merger, and a homogeneous analysis of the entire Chandra data set. We find that the late-time non-thermal emission follows the expected evolution from an off-axis relativistic jet, with a steep temporal decay $F_{ u}propto t^{-1.95pm0.15}$ and a simple power-law spectrum $F_{ u}propto u^{-0.575pm0.007}$. We present a new method to constrain the merger environment density based on diffuse X-ray emission from hot plasma in the host galaxy and we find $nle 9.6 times 10^{-3},rm{cm^{-3}}$. This measurement is independent from inferences based on the jet afterglow modeling and allows us to partially solve for model degeneracies. The updated best-fitting model parameters with this density constraint are a fireball kinetic energy $E_0 = 1.5_{-1.1}^{+3.6}times 10^{49},rm{erg}$ ($E_{iso}= 2.1_{-1.5}^{+6.4}times10^{52}, rm{erg}$), jet opening angle $theta_{0}= 5.9^{+1.0}_{-0.7},rm{deg}$ with characteristic Lorentz factor $Gamma_j = 163_{-43}^{+23}$, expanding in a low-density medium with $n_0 = 2.5_{-1.9}^{+4.1} times 10^{-3}, rm{cm^{-3}}$ and viewed $theta_{obs} = 30.4^{+4.0}_{-3.4}, rm{deg}$ off-axis. The synchrotron emission originates from a power-law distribution of electrons with $p=2.15^{+0.01}_{-0.02}$. The shock microphysics parameters are constrained to $epsilon_{rm{e}} = 0.18_{-0.13}^{+0.30}$ and $epsilon_{rm{B}}=2.3_{-2.2}^{+16.0} times 10^{-3}$. We investigate the presence of X-ray flares and find no statistically significant evidence of $ge2.5sigma$ of temporal variability at any time. Finally, we use our observations to constrain the properties of synchrotron emission from the deceleration of the fastest kilonova ejecta with energy $E_k^{KN}propto (Gammabeta)^{-alpha}$ into the environment, finding that shallow stratification indexes $alphale6$ are disfavored.
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