Yes, as it currently stands, although there’s also a few remaining BA ops to VIE they could use as well for that sector.

To the OP, while you would have the right to insist on rerouting, you don’t have a right to demand a specific airline, so you can’t guarantee they’d use OU. In particular, within Europe they have a general agreement with LH/LX/OS for rerouting, which would very likely be considered a ‘reasonable’ alternative in the circumstances.