You can work based on the fact that the online status indicates approved even if you do not have an actual document to present to the employer.  However, if you need to provide it (if the employer requires) you will need to contact USCIS and explain the situation and see what they will recommend in terms of whether they can resend a new one.  Typically they will not do this unless the first document is returned to them as undelivered but you can certainly try and as long as the address they have on file is your current and correct address, they may.