Ok, let's imagine that he doesn't know what to say to his player.. Then it's time for retirement
But it's pretty obvious that even if you don't have a 100% tactical advice than you can help your player relax a little cause he, obviously, feels the pressure after leading 9:4 and loosing 3 points in a row. Help him regain some confidence, also maybe this TO will break the opponents rhythm. This timeout may be a risk - but no timeout can guarantee you anything. And an aggressive timeout is very important cause it shows the determination of the coach.
I may be wrong. But I just can't see a reason why Jorg didn't take a timeout while Timo was loosing all those points on ML's BH serve and on his own serve too.