That is not true, our team is very weak without Stefanos, only his brother is good at doubles but that's it, everyone else is ITF level (although the young Sakellaridis seems good and is moving up the rankings a lot, he needs more time to be at a top level).
Davis Cup will be between the US Open and Laver Cup (in Canada), so I'm not sure if Tsitsipas will go back and forth to North America from Europe, but he will face a lot of criticism in Greece if he does not play so for his image he will probably do it. Also it was announced today that the Panathenaic Stadium is a potential venue for this.