What is the value of last sample of a discrete sinewave
No.  Assuming the period of the signal is N samples since your indexing is zero based the $Nth$ sample will be indexed as $N-1$.

Your signal would be modelled by:

$$ x[n] = A \sin \left( \frac{2\pi}{N}n \right) $$

Thus $x[N]=0$ and $x[N-1] = x[-1] = -x[1]$.