Permanent residency is not a visa affixed to your passport, nor does it expire when you leave the country. That’s what makes it permanent residency.
Source: am a US permanent resident.
Source: am a US permanent resident.
And how exactly do you get into the US when you return, without a visa? They won't let you in with a foreign passport unless you have a visa. No country will, unless you have visa-free travel because your country's passport is granted that.
You get into the US without a visa by having a green card instead.