You can file your extension with USCIS using the Nunc Pro Tunc (NPT) option to request for making your time i94 expiry legal in the USA. NPT application is sent to USCIS and they take their own time to process the application. It can even take more than 6 months. There are successful NPT cases for H4 when a person already spent more than 180 days in US. If you are already close to the 180-day mark, we strongly suggest to leave the US and get a visa stamp.