V2 expires while processing I-485

[alia01]

Here is my situation. I have been admitted to the US under the V2 visa (LIFE). My 21st birthday is on October of this year. I was given a visa number and have applied for the I-485 two weeks ago and discovered that it would take about one year to process my application. Therefore, my V2 visa will expire before the I-485 application is processed. My visa will expire on end of October and the I-485 could be processed by june of next year. My work permit expires in August of this year. My questions are do I have to leave the country until my I-485 is approved? If yes, how would I know the interview date and where am I to interview if I leave the country? Will the US embassy give me a visa to come here for the interview? I am hoping that I don't have to leave the country at all. Maybe I am allowed to extend my stay until the I-485 is processed. Help please