I had a similar problem and for me the Problem is with the EPSON driver.
My printer was connected wirelessly to my network, I had IP address and could ping it but WIN 7 showed it as OFFLINE.
I then went and had a look at the printer driver, (start, Devices and printer, selected the epson printer then under printer management, customise printer, ports then configure port)
And noticed that for Standard TCP/IP Port it was pointing to a different IP than that what my printer currently had. I edited it to match what the printer was and it came ONLINE.
When you turn your printer off, its IP address goes back in your routers pool to be reassigned.
The Epson windows driver still has the old IP. You turn your printer on and your router happens to give it a different IP from last time. It now doesn't match with what the Epson driver stored before and tells you it is OFFLINE.
For me, rather than changing the IP in the driver each time this happend I assigned a static IP (fixed host ) address in my router to match my printers MAC address. This way it always gives my printer the same address everytime and no more fake OFFLINE messages appear in Windows.
This is an Epson driver problem, not a windows problem.