Complex sentence: Microsoft recommends the careful division of FSMO roles, with standby (not active!) operations masters for each role-in the event of an unrecoverable failure other DCs can "seize" the lost roles.
Split into simpler sentences: Microsoft recommends the careful division of FSMO roles, with standby DCs ready to take over each role. In the event of an unrecoverable failure other DCs can "seize" the lost roles.