score:9
How likely is it that I get on as a standby passenger on July 30?
Not very likely, but that depends on the details.
This being said, there is no harm in trying. There are still a few open seats in business and if a passenger gets upgraded, an economy seat will open up. If there is no one else on the list and you find a very kind hearted agent, you may get on.
There is also no harm in calling Austrian and asking them for advice or options.
Your best bet may be book a new one way: Currently the cheapest on 7/30 is Turkish Airline through IST for about 1000 Euro.