I have to find an example of non nilpotent Lie algebra $L$ and an ideal $I$ of $L$ such that $L/I$ is nilpotent. So we can take the algebra of $ 2 \times2$ matrix upper triangular and with null trace. So the matrix $(0,1),(0,0)$ is a nilpotent ideal of $L$ and $L/I$ is one-dimentional. But... is there another example?
Your example is spot on. In general, you might take any soluble algebra which is not nilpotent. It will have a non-trivial quotient which is abelian, hence nilpotent.
In the category of trivial examples, the direct sum of a non-trivial nilpotent and a non-nilpotent algebra will do.