Then they'd have to use Samsung or Intel. Both are a bit behind TSMC, but the main issue is that TSMC has a massive amount of capacity so chips would become very, very expensive.

GPUs would go backwards a few generations for 5-10 years. Also supply shock on other industries would double the prices of chips for vehicles. Eg covid 3.0

That would not only be incredibly expensive, but there would be a period while quality catches up.