Experience as of 18s... its as fun as swimming in pool of oil or listening to doc who slowly explaining that you are having a cancer or watching two defensively playing fissures trying to grill each other. From what i remember prayer was not allowed at any period of time when i was duelling and was even more strict and tried not using more than 20 life replenish on my chars, no matter if 1v1 or tvt. Was always looking for aggressive, risky and not static duels even versus stronger opponents because its real fun.
I could imagine healdins in some mirror tvt's but as kind of capture the flag (kill VIP "firstaidkitdin") where team loose when VIP got killed, so imposing aggressive approach. In that scenario healdin must have even more strict life replenish cap to not get bored of running around blood moor in infinite loop. Maybe some more additional rules and ofc only one healdin per team cuz "If a target is within the radius of multiple auras, healing from all auras of equal level is applied". Crafted that idea right now for you, but it sound unrealistic anyway, when its even hard to get players to normal 1v1.
In short words, prayer meh for 18s.