Wait, when did the elves destroy their own well? I'm actually curious.
Only instance I am aware of is when Malfurion destroyed the Well of Eternity. And as I write this I remember how the well shaped the entire culture. I've never really thought about how the destruction of the well would have affected the entire Night Elven society. Even at this point though, the well wasn't a substance abusive addition yet.
But if this is the event you are talking about this is a completely different scenario. The well was the source of to transport demons to the world. They were there to destroy the world. The only way for Malfuirion to stop the well was to destroy it. A Highborne may have had another way, but not like they were up to the task. Also it wasn't to keep it out of their hands it was to get it out of their hands. They already had it and they were using it.
The reason I don't think they would destroy it is so long as it is there it give them power. All elves on Azeroth pull form the well. No matter where they are. This is why I think the High Elves don't want it destroyed. Even though they did not take on the teachings of kael, they were still suffering and when the Naru sacrificed itself they also would have benefited form the restoration of the well. Even though they do not live in Silvermoon, they still can draw from the well.
You state that the Blood elves have allies that can cure their addiction. Well we don't know that either. The Shal have cured their addiction to the Nightwell with the Arcandor, sure, But they soon will not have a font of energy to draw upon. Don't forget that the Nightwell is still currently active and still currently their source of power. Once that is gone I suspect they will need to learn to use the Sunwell or their magic will be severely diminished.
Also that is another reason they would not destroy it. That is THEIR source of power. Cure the addiction, sure, but now what to do about magic itself. Their's will fade away if they do that along with their chance to take the well back form it's captors.
Wayward traitors. I have never looked at the Silver Coven/High Elves as traitors to the Blood Elves. They saw something that was gruesome and decided to not partake. They left. They didn't join the Alliance (just barely I'll admit), they are officially neutral. Granted they were a little too happy ti round of the Blood Elves in Dalaran after some special events went down.
Paladins. A subset of the blood elves, but one of the top brass in Silvermoon is the paladin leader whose name I'm not going to butcher at the moment. The moment you cut them off from the well, they are no longer Paladins. They originally got their power from a Nar, and now they get it from his sacrifice into the well. Just no.
It would be a huge mistake for the Blood Elves, or any elves other than the Kel's to destroy that well.