When people think "Adoption", they usually think about some sort of meritocracy, something partially due to a network of really favourable Roman scholars that did their best to say that "everyone before was dirt, and that everyone now were benevolent genius, and we didn't recieved any kind of pressure, no siree, not even threat of using this torture device with the thingie with a metal point and traces of fresh blood on the other thingie with a wooden plate that I never seen because nobody threaten me at all".
More seriously, Antonine dynasty in spite of its adoptive succession wasn't wholly different from Julio-Claudians for exemple (remember that Nero, for exemple, was adopted by Claudius), or even Tetrarchy on some ways : not only because adoption wasn't just some formal device but complying to a strong political desire of dynastical succession (
genius and
virtus being less associated with individuals than with a gens or even a familias); but as well because these persons were often related trough familial links : blood or marriage.
Hardian was the closest male relative to Trajan, for exemple.
Eventually, the strong link that adoption was (enough to build a dynastical succession, again, not just something formal) could continue but wouldn't be at the slightest an UFO.
Assuming Lucius Verus survives ITTL (and, in order to underline the previous point, remember his father was supposed to became emperor himself) and giving the increased military pressure coupled with a "civilian" (senatorial, mostly) dissatisfaction...
I think that the ongoing trend of rebeliousness and court plots (that already popped up by Marcus Aurelius' reign, contrary to previous ones since nearly one century) wouldn't stop : the general crisis (outer and inner, as with the epidemics that ravaged the Empire, but as well political struggle), meaning more infighting , possibly devolving into civil war not unlike it happened IOTL.
So, giving a good part of the Third Century crisis was due to factors that Romans hadn't the slightest grasp on it (Climatic changes, Epidemics, Barbaricum political reshuffle) and to others that pretty much were already pregnant (as dynastical struggle), I don't think the crisis would have been butterflied at all but its prime context could be handled differently.
Let's assume, for exemple, that the dynasty survives, probably having cut out some branches (Commodus, Verus, Pompeianus, Balbi?, etc.) against revolts and usurpation, it could have gave them enough legitimacy to live on one way or another (altough I suspect non-adoptive succession would be more common to avoid giving other people too much legitimacy, it would more than probably survive).
Probably a bit more political stability (compared to Severian) that could help making the Third Century Crisis less an existential threat, but many political trend would still appear (more or less modified) at this point. But Antonine dynasty would still undergo similar issues of growing trend of usurpation and revolts, as well dealing with crisis that if minor compared to the IIIrd century, would still be a problem.
That is, by definition, impossible I'm afraid.
Things doesn't continue indefinitely without any regard with the context : Antonine dynasty fit a period and eventually its structures would stop doing so. Either it continues until meeting the hard harsh wall of Reality, or it adapts (and even there, would likely meet an end).
In other words, sooner or later, Antonine dynasty would have known an end as all of its predecessor or successors.