Should i keep my US greencard valid ?

If you stay outside the US for a year, you'll lose your immigrant status. If you check with the consulate nearest you, ask about a Re-Entry Permit, a document that will keep you in status for two years. After that, you have to decide what's best for you.

I don't think the US economy will stay bad indefinitely. But giving up your immigration status won't guarantee you a normal visitor visa.

If I were you, I'd keep my status by visiting the US (using your I-551) at least once every eleven months. You need not stay long, but make sure your passport documents your physical presence in the USA.

If you finished high school and began college, you might have met the residency requirements for US citizenship. As a citizen, you can live outside the US without worry about being able to go back. The rub might be India- would India allow you to become a US citizen without giving up your rights to live in India? Good luck!!

To keep your status you have to live in the US .... having a home and job in another country will get it voided

if you stay out over a year it gets voided

you can get a Re-entry permit while in the US ..which will give you 2 years out

but as you say the US economy is bad

You're in the Canada section. I think you want the US one. Canada doesn't issue green cards.