I have argued elsewhere that we cannot really know with accuracy any of the sayings or events of the Buddha's life or teaching. At best we have shadows of shadows.
We might expect that the Last Word’s of the Buddha would be exempt from this lack of certainty and authenticity but, alas, this is also not the case. There are countless translations and interpretations and suggestions as to the Last Words and no way to know if any of them are authentic.
What we can see is that the meaning of the Buddha’s last words, in all various instances, can be divided into categories.
The first grouping of meanings captures the centrality of Impermanence and the necessity of diligence with regards to Dharma. This meaning of the Last Words comes from interpretations of the Maha Parinibbana Sutra and has such examples as:
The Second set of purported Last Word takes a more radical tone, especially when compared with the rigid orthodoxy of Buddhism as it is today. In this version the Buddha's Last Words implore a global scepticism (As in the Kalam Sutra) and self-guided path towards one's enlightenment and happiness.