The maximum time past due date before you need a new SIM card seems to vary depending on factors only known to Tracfone. If you power up the phone and get the SIM card unknown message, then you'll probably need a new SIM card. You can try reactivating online with an airtime card first just to be sure. IF you need a new SIM, the online screen will tell you so and give the number to call. The SIM cards are FREE, just call Tracfone's customer service number and tell them you're reactivating an old phone. They'll ask for the zip code of activation (pick the one you want based on your map studies), and a name and mailing address to send it to. They won't send it to a PO box. You will have to have someone be home to SIGN for the package. It will probably be sent via DHL package delivery. Then you will need at least a 60-minute airtime card in addition to the SIM card to reactivate the old phone, but it should go smoothly with an online activation after that. You won't be able to get the 20 minutes free for activating online though because it's not considered a new activation. Ditto for the RAF program that technically doesn't exist anyway... ;-)
According to Tracfone's TOS, I think you get about 60 days past the due date to simply add another airtime card without having to reactivate with a new SIM card, but like I said, stories vary wildly past that point and your mileage may vary.