It seems that Rameses II defeated them and selected some of these warriors for his personal guard.
They have been associated with Sardinia, principally for two reasons: primarily, "Sard", the obscure linguistic root of the name of the island (most of the ancient history of Sardinia owes important passages to this science) might come from the name of this people, perhaps both being related with the name of Sardis, in Lydia (but there is a different theory that derives the name of Sardis from "Shfart", allegedly related with Sparta). Secondarily, it is commonly supposed that the mysterious civilisation of Nuragici people could have come from other areas of the eastern Mediterranean sea (it is quite commonly agreed that Sardinia had no autochthonous population), the same areas from which it is supposed Shardana could have come from, due to particular retrievals or discoveries (in Anthropology too) which showed notable similarities in the two regions.
Proposers of these theories (that include archaeologist Giovanni Ugas and - even if not explicitly - Prof. Massimo Pittau, who suggests at least an assertive assonance in calling the first Sardinian language "lingua Sardiana") stress that at the time of Obsidian commerce, Sardinians necessarily had to be skilled sailors, having reached France and northern Africa: notably, among the many archaeological retrievals from nuragic civilisation, there are some ships, in fact, whose essential elements could recall some elements of the later phoenician ships.
Moreover, in a very distant field, recent studies by geneticists on the DNA of inhabitants of the inner areas of the island, tend to confirm the presence of some elements which would be in common with those of people from Anatolia; this has been seen as a further step in the direction of identifying the provenance of ancient Sardinians from a determined area of the Mediterranean.
The fusion of these theories invites to conclude that a people of skilled sailors left from Eastern Mediterranean to reach Sardinia and established themselves there. They very probably could have found some resistance in their way to it, or it is also possible that they were explorers, so it is likely that only a warrior people, like at that age Shardana were, could have organised such an expedition, therefore some theoretical coincidences (enforced, as said, by linguistic considerations) could allow to assume that Shardana first populated Sardinia.
Honestly, historical dates and ages of the few proofs of their existence could not be completely compatible with these suppositions, which would require that Shardana had travelled well before the age of obsidian commerce, but it is also true that the said fragments in which Shardana are named could have been copies of previous documents, or simply talking about previous facts (or legends). Also, the proposed relationship with the people of Sargon (or Sardon) seems too recent (2450 BC), still with reference to the obsidian commerce.
Time differences, more probably, could rather reveal a certain interaction (or even a coincidence) between Shardana and Nuragici people. In this sense the alleged similarities could find a more concrete confirmation, and the assault against Cyprus, described as brought by Sardinians in Simonides of Ceo's scripts (as reported by Zenobius), could allow this hypothesis.
Anyhow, little serious literature is available on the topic, due to the very few valid elements available; most of what recently published seems to be more related to local nationalistic or however political purposes. Perhaps, the most serious discussions might regard some hypotheses that have been proposed about the supposedly related origins of Vikings' ships.
This theory has however been discredited by some authors.