Nothing To Worry!! You are safe Side
Hi
As you are I-140 Approved, and 485 pending > 180 days you are safe side.
Here are two Choices for you.
1. Wait until your Company Closed down and find Similar JOB and Same or more Pay JOB and apply AC21.
2. Immediately find Similar JOB and Same or more Pay JOB and apply AC21.
Both lead to AC21, Only thing is you need to decide, if you want it to do now, or Wait until Company announce the Closing and take step after That.