I think that depends what you mean by "biggest", as the US is richer and both India and China have more people. I think Apple sales in China and the EU are about equal, and that US are significantly higher, but my info may be out of date and was merely a summary in any case.

But I would agree, they're not likely to just give up on the market. Even ignoring the likelihood of similar laws everywhere else, it's too big and too tempting.

EU's a very large, very wealthy market, but not the biggest for Apple. https://gs.statcounter.com/os-market-share/mobile/europe Android owns more than 60% of the EU market. Even so, writing off the EU would be further knee-capping Apple's global market share, and would for certain constitute a more than 10% drop in revenue, and not just for this year, for all years going forward until they find a way back into it. So no I don't think Apple's going anywhere.