The League of Assassins has been in existence for centuries. A group of trained killers whose sole function was to eliminate dangers to society, they served no other function. These are men and women who have no other purpose than to kill. Because of their dedication to Ra's al Ghul they don't know how to live their own lives. So when Nyssa al Ghul disbanded them, they were left to their own devices, which can't be good.
The League of Assassins only pledged allegiance to Ra's al Ghul, so now they must either find a new master to serve (which I fear might be the case) or fall prey to their own misguided sense of right and wrong. With thousands of warriors, the League is a ticking time bomb, even if they are scattered across the land now.
In the television show, Nikita, a group of government assassins were released from their duties and dozens went rogue, becoming killers for hire. In that scenario, the assassins had to be hunted down and eliminated to erase the threat to mankind. Now imagine having to round up even half of the League. Unfortunately, I see a worse fate awaiting them.
We all know how much Malcolm Merlyn craved the power of the League, and since he still wants the ultimate revenge against Oliver, reorganizing the League makes sense. Can he do it without Ra's al Ghul's ring? Is there another artifact or piece of magic that would give him the ability to restore what he's lost?
I can't imagine Malcolm simply abdicating that power without fighting for it. He has always had contingency plans. Remember he had two earthquake devices in Season 1 to make sure the Glades was obliterated? He also had the despicable plan of using Thea in order to get out from under Ra's al Ghul's blood oath. With Merlyn headed to DC's Legends of Tomorrow, it's entirely possible he will attempt to return to the past when the League of Assassins was still intact.
Of course, Ra's al Ghul is still alive in the past, but Malcolm knows how to defeat him now, and he is conniving enough to use every ounce of knowledge he's learned to return himself to his former glory. The Dark Archer isn't someone who can last very long without power at his fingertips. With his fortune all but gone and his power stripped away, Merlyn will be looking for a way to rise to the top again.
While this is all supposition, I find it hard to believe that thousands of men and women can disappear without any repercussions to the Arrowverse. Whether those repercussions come in the form of rogue assassins or a reconstituted League courtesy of Malcolm Merlyn remains to be seen. At this point, it's difficult to imagine thousands of killers are gone for good. Even more, it's unthinkable that Merlyn won't try to regain what he considers to be rightfully his.