I doubt, the roman can win, once Varus walked into Arminus' trap.
But the Battle of Teutoburg Forest could had been avoided by avoiding the Pannonian War, or Varus decides, that it is too late in the year to start a campaign and marches back via the Lippe-Route to his winter-camps. I doubt Arminius is risking to attack them on this route. This would end in an open field battle, he can't win. Perhaps Varus even exposes Arminius as a traitor, tortures and kills him.
This would not prevent battles in the Winter 9 AD, and the romans would loose many units spread all over Germania. But the romans lost units, even complete legions, more than once. This is not comparable with the shock, after loosing 3 complete legions plus auxilia. There was already an "immensum bellum" around 1 AD. Unfortunately we know no details about it. But the romans did not surrender. Without this huge shock, which forced the romans to restart their conquest almost completely, and to rethink their strategy to defend Gallia from scratch, they would not abandon Germania that easily.
This would also not avoid that the germans tribes would revolt in the future. Germania is still far away from pacified. But remember huge parts of Germania did not participate in Arminius War. The South was still safe. The Hermunduri and other southern tribes like the Mattiaci remained loyal. Also the Frisii and the Chauci in the very North did not participate in Arminius coalition. Same with the Langobardi at the Elbe, who were more allied with Marobodus and his Marcommanns. And Marobodus remained a loyal client, too.
With ongoing trouble in a a rather unsecured Germania, emperor Tiberius himself would perhaps see the need to lead the campaigns onsite for decades. Tiberius strategy was fully different to Germanicus' strategy. And he was the way more experienced general. Tiberius mastered divide et impera, with a mix of diplomatic and military actions. He always tried to strengthen the rome-friendly parties in the tribes. Young Germanicus did more bad than good with his brutal attacks. This way the romans lost all support in the german tribes. At the end Germanicus won nothing and lost perhaps more soldiers than Varus. Perhaps the main reason, why Tiberius called his incapable general back to Rome.
In the long run, the advantage of the Elbe border is not, that less germans are rest between Elbe and Vistula, even if less attackers are always a nice thing. But that way more germans become germano-romans. The germans would probably supplement or even replace the illyrians as the main pool for roman legionaries after romanization and we would see an emperor with german roots sooner or later.
I agree that it is highly unlikely, that the romans would conquer all Germania up to the Vistula. The regions east of the Elbe were even more of a nightmare than western Germania. Fortunately also less populated. But perhaps the romans would annex Marcomannia around 50 AD. Until then the Marcomann King Vennius was a vasall of Rome, but he was brought down by his nephews. Or the romans would intervene even earlier, when Marobodus was brought down in 18 AD. If the romans are more engaged in Germania, they would deal differently with Marcomannnia, than they did IRL. This way the border is further shortened, especially after Dacia is conquered.
Another important point is, that with ongoing trouble in Germania, the romans would not invade Britannia and waste 4 legions and the biggest auxiliary force of the empire for a small island in the north. They would have found less costly ways to secure the channel border. Perhaps a Classis Gallica. And with 40.000 men more in Germania, I am confident, that the romans had good chances to keep Germania, romanize and pacify it finally.
I also do not see civil wars. There were not that many usurpations during the principate until Severus Alexander. Actually just 2 critical ones after Nero and after Commodus. 2 major civil wars in 250 Years is not that much. It is even unlikely, that in this alternate history Caligula becomes emperor. Perhaps Drusus the Younger does not die in prison, because he is campaigning with his father. And of course Germanicus may not die in Syria. And if the julio-claudian dynasty does not die out (that soon), and/or brings no overchallenged "kids" like Caligula and Nero to the throne, the first civil war is butterflied away.
Of course there is a lot more to do, to avoid the 3rd century crisis 250 years later. The crisis is based on external threats, which are reduced somewhat now, and rather detrimental internal changes of structures in military, society and economy, which are harder to adress in a plausible story than just conquering a bit of Germania.
