Well sooner or later the Rouran will fall to some sort of upheaval. The ease with which they were displaced by the Turks speaks to some serious problems within their state, brought on, likely, by failed wars with China and also just demographic shifts and climatological factors that will be difficult to butterfly away.
The Rourans were, by all accounts a tiny part of their broader union, rulers in a very confederal state. Accordingly they were forced to make a lot of compromises and themselves were not very strong.
I don't think any of the Hunnic migrations will be stopped by a continued Rouran, since I don't buy that the Hepthalites or any of their cousins were under Rouran hegemony, but the Avars and Turks will have their trajectory altered. (The Avars will likely never exist) It seems likely to me that continued Rouran dominance would just ensure a totally different set of tribes and language groups come into power in a few generations. Maybe the Tiele or the Gaoche? An Iranian language might well remain prominent on the steppes far longer. Regardless, the character and culture of the steppe will be very different.
Now, to answer your question, since the Kushan and Kidarite conquests of central asia already happened, not too much will have changed. I'd be wary of saying that undoing the Hepthalite conquest is a good thing, because I believe Central Asia started recovering under the early Hepthalites, and before that point, urban society and agriculture had declined significantly. Then again, it's possible that the cities of Balkh and Sogd and Gandhara would have begun recovering on their own under the Kidarite rule. We just don't have enough understanding of Kidarite governance and policy to really make a clear statement, beyond the fact that they tended to imitate the Kushana in most things.
Butterflies might see Kidara survive. They were almost certainly beginning by the end of their existence to settle down en masse. They'd long had coinage and fixed temples and capitals and all the other trappings of a sedentary civilization, it was only a matter of time. If it does, the Sasanians are not going to be much stronger, because they'll have a major power on their back. And since the rise of the Gokturks was a (in)direct threat to the various Hunnic states, averting it averts a major threat to the powers that be in central asia.
By averting the rise of the Turks, you do however avert some of the migrations that are very familiar to any student of the migration era. By butterflies you can pretty much say good-bye to anything coming from the East in a recognizable form.
As long as the Rouran are around, the energies of their subject peoples will be focused on overcoming them, so that whichever subject successfully overthrows them can lead the confederacy. This is a problem for the Rouran because some of their subjects, like the Turks, are far more numerous than them. However on the flip side, it's a boon for the settled world because now the various Turkic tribes are busy punching up.
The one last thing I'd add is China almost certainly should be made to do worse in this scenario. Part of the reason the Rouran collapsed in the end is that they didn't fare well in their wars against China.