The charges were only dropped on a technicality because prosecutors were unable to formally notify him of the criminal allegations against him. It was not because the victim changed her mind, or because the prosecution did not find the claims credible.
As a result, when announcing the decision to drop the case in 2017, the Swedish Director of Public Prosecutions Marianne Ny deliberately reminded the public that she would be able to reopen the case as soon as Assange " makes himself available."
Now he has left the embassy and is in custody in Britain, the Swedish authorities could very easily notify him of the allegations against him. They have already received a request to reopen the case and will likely do so.
The Swedish case was opened before the US case. Therefore, it should take precedent should Swedish prosecutors decide to reopen it.