The Valiant was a UK comic, published by IPC Magazines, which ran from 1962 to 1976. The story I am looking for details of followed the adventures of a group school kids and their teacher in an Earth that was deserted.
Turns out they didn't disappear because at school they were doing some science experiments on some meta (called delirium?) I'm pretty sure the comic must have been around 1966 (certainly it was before its merger with TV21).
One of the stories in the arc was set in a zoo, where the animals escaped. It turns out the animals didn't disappear because the bars of the cage were made of delirium (?). Turns out that the Earth's population were made to disappear by aliens who wanted to have the Earth for themselves.
I forget the reason why, but the aliens (out of the goodness of their heart or perhaps even hearts) decided to reverse the process and return the Earth's population.