There are still daily flights to and from USA in Frankfurt:
I could also see the different teams chartering a plane in a joint venture and bring back their players - plus some cargo maybe to lower the costs But then again, these players need to go into quarantine first, can't train etc. So this is all but easy.
https://www.google.com/amp/s/nymag.com/intelligencer/amp/2020/04/heres-why-so-many-planes-are-still-flying-nearly-empty.html
Now most countries have closed borders, so travelling is impossible. And when it will be opened, it will be difficult to collect players from different parts of USA with limited flights. And then as you say, they would have to spend 14 days in quarantine after that.
Quite many players like Mike James from CSKA said that they are against resuming season. So, some teams probably will have to play without full squad.
They are playing most games in sold-out 15k people arena and money from tickets is almost 40% of their budget. So, playing without fans would hurt them badly.