Go through India airspace?I don't think India would give China permission to do that
And even if you can bomb Diego Garcia,the US still has plenty bases in the Middle east and Africa,all of which could strike Chinese ships
China can go through Myanmar.
And note that China has actually built airfields in Myanmar.
Also, I highly doubt that countries in the Middle East or Africa will allow US bases to be used to attack Chinese ships or territory. Remember that even today, DF-26 class missiles can cover all of the Persian Gulf waters and adjacent oilfields and oil refineries.
And those countries know that:
1. The Chinese economy is approaching 2x the size of the US economy in real terms
2. In terms of manufacturing output, China is more than 2x larger
3. The US Navy says China has 232x the shipbuilding capacity of the US
4. China is their largest trading partner, and this will likely remain true after any conflict ends
So please think about what realistically would happen, instead of clinging onto unrealistic scenarios where the US wins.