I own one of these, but it´s currently not in use. My use case would have been an OpenBSD machine, but due to lack of support (either from OpenBSD or from ROS side), I couldn´t use it. First OpenBSD compatibility was announced, then it disappeared from the MT materials. It works OK with Linux, but not with Win or not with ESXi.
http://forum.mikrotik.com/t/ccr2004-1g-2xs-pcie-and-freebsd/159742/1
As for using it offline, just with a dummy PCIexpress adapter card: I tried it once, since it has pretty decent HW. Could be useful as a replacement for an RB5009, though there is no USB port.
My experiment ended with blowing up an elco on the PCIe adapter board and also blowing the SMD fuse on the CCR. Then I decided it´s a waste of time, though I believe the culprit was the cheap PCIe board and the card might have worked. I could repair my card though by replacing the blown fuse and I tested it with Linux.
http://forum.mikrotik.com/t/ccr2004-1g-2xs-pcie-blown-fuse-would-need-specification/161016/1