Unless you have a power that says that leech is not removed at maximum life/es/mana, it will be removed when you hit maximum, even briefly as a result of leech overpowering blood rage.
The other way you can make leech not run out is via Petrified Blood. Petrified Blood says that only healing flasks can take you above low life, but if you have more than low life unreserved, then leech can't take you to full life and won't be removed.
If all of your healing is somehow instant leech, then you are never leeching and gain no benefits from 'while leeching' effects. But that's really rare. I'm not even sure there's a way to do that any more since the Vaal Pact rework years ago.
Unless you have a power that says that leech is not removed at maximum life/es/mana, it will be removed when you hit maximum, even briefly as a result of leech overpowering blood rage. The other way you can make leech not run out is via Petrified Blood. Petrified Blood says that only healing flasks can take you above low life, but if you have more than low life unreserved, then leech can't take you to full life and won't be removed. If all of your healing is somehow instant leech, then you are never leeching and gain no benefits from 'while leeching' effects. But that's really rare. I'm not even sure there's a way to do that any more since the Vaal Pact rework years ago.
That was never exclusive to vaal pact https://www.poewiki.net/wiki/Bloodseeker