H-1B Amendment and Existing Visa Validity

I had a existing petition till Jun’2019 with valid I-94 till Jun’2019 but recently my location change amendment was filled which got approved for the new location till Dec’2018 and with new petition, there is no new I-94 sent by USCIS.

So my question is will be old petition will be valid after by existing petition will be over in Dec’2018 and Can I continue in US based on my old Petition which is still Jun’2019 and Can I travel outside US in Feb’2019 and come back in Mar’2019 and in between file the extension.