How do I obtain a permit for my parents

[Kassie]

My parents are on a GC. They left the US 8 months ago to visit India. While there, my father fell ill. He is recovering and still not in a position to travel. Since they can not stay for more than a year, I assume they need to apply for some sort of permit. How do we do that? They were told they could only get the permit if they come here which they can not in my dad's current health. I would appreciate an answer as soon as possible so we can get the paperwork going so they don't lose their green card.

[Enub4]

Maybe this can help:

https://travel.state.gov/content/travel/en/us-visas/immigrate/returning-resident.html

I hope your father gets well soon.