Pass over to the other side
Euphemism for dying.
'Passing over to the other side', or simply 'passing over' is a euphemism that has its roots in the Bible and the Christian belief in a heavenly afterlife. This is well illustrated in an early, perhaps the earliest, use of the phrase in print, in John Bunyan Pilgrim's Progress, 1684:
When the Day that he must go hence, was come, many accompanied him to the River side, into which, as he went, he said, Death, where is thy Sting... So he passed over, and the Trumpets sounded for him on the other side.
It isn't surprising that Bunyan used, or possibly coined, the phrase 'passing over'. He was of course a devout Christian and would have been a believer in a literal heaven. Also, the theme of Pilgrim's Progress, which is fully titled 'The Pilgrim's Progress from This World to That Which Is to Come', portrays the progress of the devout as a journey ending in the crossing of a river heading towards Heaven.
See also: 'Pass away'