「……っしゃ！ ずらかるぞ！！ ……ん！？」
Is it a colloquial form of 「よっしゃ」?
It is just an abbreviation of 「よっしゃ」.
Probably ninjas or thrives completed their duties and didn’t want to show their acclamation in order to break out swiftly. That’s why they said っしゃ as explained in the other answer.
As a side note, I’ve never seen った as やった in the same vein. It might sound like ouch, however.
