May not be what your problem is but I have an HP Wireless Printer that did not necessarily disappear from my network but kept reporting that ' Wireless Scan to PC ' was not available and I would be unable to connect to the Web Interface for the printer. A reboot of the printer would normally start things to working again.
My particular router has an option called ' APSD ' and another option called ' MSDU(A-MSDU) ' that fixed the problem when I enabled both of them. Never did go back and test to see which one actually fixed the problem.
You might dig around in your router to see if you have anything like that.