Nepal ko Keto,

What you heard is wrong. this happened to one of my relatives too and they gave him 1 month time to return even if his 6 month stay visa had expired. If denied, USCIS will send you new I-94 with enough time frame for people to leave.

Now a days, the processing time is very late. My parents extension Approval letter came after they left (left within 6 months of extra extention). Approval letter came after 8 months only. With their old expired I-94 they returned. But now they are here again. No illegal. because USCIS will have all in their system.

The main thing you have to keep in mind is the extension period  i.e till what date you wrote on Extention form I-539 that your parents will stay here? It should not be more than 6 months from the previous visa expiry date (i.e if their visa is till October 30 2008, you can extend till April 30 2009)

If they stay beyond that extended date of April 30 2009, waiting for approval, they will be illegal. The reason for this is if you get Approval letter even after 10 months, USCIS will send new I-94 with visa till April 30 2009 only. Because that is what you wrote on Extention form. 

If you have written April 30 2009, the last day of your parents stay in USA, USCIS expects them to leave on or before that day. USCIS doesn't think that your parents are still waiting here for it.

 Your parents have to return before this date even if the extention is pending. They can go back with old expired I-94. They will not be illegal.

Most of the denied letter come before the extention date expires with some time frame to leave. USCIS does not make anyone illegal. Unless you yourself are ignorant to keep track of the dates.  

nepali.chicago,

If somebody has 5 year multiple visa, then they need not go to embassy everytime they return from USA. Only after expiration of 5 year visa if they want to come to USA again, they need to reapply for visa.

Call USCIS customer service. They will answer it.

There is another one office too which you all might don't know. It is called CUSTOM and BORDER PROTECTION OFFICE. USCIS and CBP are connected. If you want to know about your old I-94's you can call CBP. . The staff at Port of Entry who interview us all belong to this CBP. They also give lot of information mostly regarding I-94.