Sidious's actions in those scenes are pretty clear. He underestimates Yoda's power at first. When he's able to blast him against the wall with lightning, he thinks that he's got the fight in the bag. Then, Yoda gets up and Force pushes him across the room. Palpatine realizes that there's a chance he might lose the duel, so he decides to run and let the clones deal with Yoda. After all, at this point, he's got a lot to lose. He's won, the Jedi are all but extinct and he's the Emperor. Since he can't win easily against Yoda, he decides to just leave and summon the clones to kill Yoda. When Yoda blocks his escape, he has no choice but to fight. So fight he does, and they're almost evenly matched. Palpatine wins in the end, but it's closer than he'd probably like. It would have been safer to run and let the troopers hunt Yoda down. In the end Palpatine still wins, he remains Emperor and Yoda has to run for his life, without lightsaber and even his cloak. I'd call that a Sith Victory.