The fragility of Daemon Princes is their achilles heel. Any S10 can double tap them out (unless they pay an obscene amount of points for a coin flip at getting the Biomancy Iron Arm power), and really, how hard is it to inflict 4 wounds to power-armored T5?
Ground them (preferably with AA weapons so you have a good chance to hit, then scraps like rhino storm bolters if need be, then by any units you've cast Prescience on or that have twin-linked weapons) by whatever means necessary, and then dakka or Vindi pie-plate them to death. Maybe yeah, they'll kill an enemy unit. If that's the sacrifice you need to make to kill their unit, so be it.
What sphinx of plascrete and adamantium bashed open their skulls and ate up their brains and imagination? Imperator! Imperator!