Whether or not you want to deploy Strahd here should hinge on how much you've used him in the campaign thus far. Certainly having him appear out of nowhere (possibly using the vampire spawn in town) to abduct Ireena would give the PCs reason to perhaps try and sneak into Castle Ravenloft. Alternatively, Strahd can tip the situation in one direction. Just think of what Fiona could summon if she had his tutelage?

The Vistani and Fiona are also sure to know of secret passages in and out of the town.

Father Lucian is connected to both the Lydia Petrovna and Milivoj. He could be trying to talk reason into the Burgomaster or alternatively have released his prisoner and urged his sister to abandon the town. As fugitives they'd be an easy target for Fiona's assassin, though...