I've been watching Kings and General's series on the 30 years war and it surprises me how Austria can spend 30 whole years under attack by powerful neighbors and not collapse. Their lands were occupied, people were scattered, and even nobles would scheme together against the interest of the emperor, like killing off good imperial commanders.
Someone else may be able to expand on this more, but as I understand it:
While Protestant/anti-Imperial forces did threaten Vienna very early in the war, in general the war did not reach into Austria proper, which limited the devastation and financial damage Austria suffered.
Austria was fairly powerful and wealthy in and of itself, and was further supported financially by Habsburg Spain, drawing on the wealth coming from its colonial empire.
Austria, acting as Holy Roman Emperor, was not the only power in the war. The Catholic League, an alliance of Catholic princes in the Empire led by Bavaria, also shouldered much of the burden (in manpower and funds) of the war.
Armies from the time on all sides tended to “live off the land,” acquiring both supplies and pay by looting towns and cities. That provided an alternate solution to financial issues, though obviously led to problems with the locals.
As for nobles killing off good Imperial commanders, are you talking about Wallenstein? As far as I’m aware, the Emperor arranged for his assassination, or at least wasn’t trying to stop it. Wallenstein had already been dismissed once, as the Emperor feared his ambition - as a powerful, wealthy noble with a large and successful army which could become personally loyal, he was a threat to the Empire as well which led to his assassination.