Well I just glanced thru the FSM and what I came up with is that there are no fuses for the rear defogger, only a relay which I believe is integrated into the IPDM E/R (box under the hood with relays and fuses).
If the rear defogger relay is in fact integrated into the IPDM E/R box, the relay itself can't be removed.
You would need to replace the entire IPDM E/R unit.
However the relay may not be the issue anyway...
Look at the troubleshooting chart here in the FSM on page 85
http://boredmder.com/FSMs/Nissan/Maxima/2008/GW.pdf
And here for info about the IPDM. Page 17
http://boredmder.com/FSMs/Nissan/Maxima/2008/PG.pdf