The trinity is just a name for a process that involves more than one player. One player takes damage, another heals the damage taken, and the last does damage. At a high, abstracted level like we discussed pages back, it's just a process that involves multiple players shifting sets of numbers around from each other to the mob. But the key point, the key mechanic, is that this shifting involves more than one player working together: it requires multiple players working as a team to shift them efficiently.
Because one player can't shift these numbers alone, a 'role' in this process is realized. And this role means something specific: you cannot perform other activities involved in the process because those activities are reserved for other players, otherwise there is no teamwork, no working together.
If they get rid of the trinity as we know it, the question to ask then, is what process that involves multiple players will that be replaced with? You have to replace it with something - that is, if your game is numbers-based like every other rpg ever made, then you have to create a process that forces players to shift these numbers around as a team. You can't remove it and put nothing in its place. You cannot give everyone a piece of every role and expect it to 'work out'. You need a specific, systems design-oriented process in place that forces players to play ONE part in that process of shifting numbers, else whatever mechanics you have will not be a better design than the trinity.
