The green card process can take 9 to 20 months and applying for a green card demonstrates an intent to immigrate so it's highly likely attempts to return on other temporary visas like a student visa will be denied.

So they likely have to wait out the green card process abroad unless they secure a dual-intent visa like an H-1B.

There's also 75 countries that the US has shut down consular processing for so those people may be locked out getting a green card entirely.