when a company goes public the founders and original investors cash out some percentage or all of their investment. So Dikshit and the rest of the founders were guaranteed to have a hundred million in the bank the day party IPO'd. So the ownership of party is spread among alot of people now. Hence, the managers dont have as big of profit incentive as a private company.
There was alot of risk in Party staying in U.S. Losing 50 percent of the company's value is bad but not as bad as the company being completely shut down etc. In alot of ways i would think being public would make a company's management alot more conservative (shareholder lawsuits etc.)
So yeah i think Party's decision mostly is grounded in being a British public company.