Without this bug-eyed emperor’s edicts of 380-91 AD, the Delphic oracle would still be in operation, the Olympics would not have had to be reinvented in the 19th century, you could still hire a diviner to read your sheep’s entrails, and the Vestals would still be preserving their virginity in Rome.
Pagan libraries might still be open, having taken better care than the Byzantines to preserve more than e.g. a miserable seven masterpieces by Sophocles, who wrote ten times that amount. If Theodosius hadn’t banned worship of statues there would be a lot more with complete heads and arms for classical art historians to discuss.
Theodosius also banned conversion from Christianity to paganism, which was still happening---it wasn’t only Julian ‘the Apostate’, the last pagan emperor in the 360s, who was brought up Christian but fell in love with the Olympian gods.
Pagan rites did rumble on for a while. As late as the sixth century, some Greeks were still worshipping their bloodthirsty Artemis on the south coast of Turkey under her resonant title ‘Artemis of Freedom’. But it was Theodosius who ensured that the ‘ancient Greeks’ were now running their last lap. Just to be sure, he invented feudal theocracy by submitting to the orders of Bishop Ambrose rather than insisting that as Emperor he do anything he pleased. The world today might have been very different if Theodosius I had lightened up.