you should be good with printing a copy from the website or requesting an appointment to get an stamp on your passport

But is it possible to get again I-797 Extension Letter?

no is not

they’d say u have a copy on the online account

If this happen to me I will call them and ask them to resend me another original extension

hello, please check your USCIS online account for a copy of your extension letter. If you call, they will tell you same unless your extension has expired then they’ll have you come in for a stamp.

how much longer are you waiting for a card ?