To simplify this expression, we will first expand the last term:

(a-1)(a+1) = a^2 + a - a - 1 = a^2 - 1

Now, we substitute this in the original expression:

(a^5 + 2a^4 - a^3) / (-a^3) + (a^2 - 1)

Now, divide each term by -a^3:

a^5 / -a^3 = -a^2
2a^4 / -a^3 = -2a
-a^3 / -a^3 = 1
(a^2 - 1)

Therefore, the simplified expression is: -a^2 - 2a + 1 + a^2 - 1 = -2a.