There are various ways in which people leave EVE, but there is usually some sort of correlation between the discard of their in-game wealth and the permanency of the departure.
I think people trying to make a clean break can lean towards sabotaging the option of return – giving away all their ISK and assets, or taking the next step to sell or transfer their characters to those who remain in the game.
I had a quick thought – I wonder if the skill extraction process might make really leaving the game a little easier? Rip all the SP out of your characters and give away the proceeds, leaving you unenthused to return to the penniless shell of your former character.
Of course you can also just trash and biomass everything.