It depends on whoever comes into power. Even without the Romans, things were going to the crapper especially upon the death of Antiochus II.
The problem is the frontier is insanely difficult to defend fully. I think the state would have had lots of rebellions and eventually fall victim to the decay it had in OTL if it doesn't just go out with a bang in the midst of multiple heirs. Did Seleucus have more than one son?