The first episode of sequel series Ashes to Ashes shows that the protagonist, DI Alex Drake of the Metropolitan Police, has been studying Tyler's notes and 2008-era personnel file, in which his photograph is overstamped with the word "SUICIDE" - consistent with what happened in the series finale.
In the final episode of "Ashes to Ashes" a fuller explanation for Sam Tyler's experience is provided, when the role of Gene Hunt in both Life on Mars and Ashes to Ashes is revealed.