The tier 7 Lich passive ‘Darkguard’, which states “Grants (7/14/21) ward on critical strike.”, does not provide any ward on a critical strike.
Esaily tested through multiple launches of the game. The character on my account “HCPractice” is spec’d into the Lich passive skill “DarkGuard” with 3/3 points. I have zero other forms of ward generation if I do not cast ‘Mark of Death’ on the target. So ignoring Mark of Death and criting targets hundreds of times has produced 0 ward