No FMC, no RNAV capability. Therefore not approved to use european airspace flying IFR except with special permission by every concerned ATC unit. So inform ATC and ask for vectors to the next airport.
Judging from our OFPs (LIDO) it isn't required anymore to have all waypoints or even all airways on it and therefore is not usable for navigation.
Actually had a case of FMCs being unable to "talk" to the rest of the airplane which resulted in autothrust always trying to achieve 104% N1 regardless of actual speed and MCP selected speed. If the same is true with completely failed FMCs you probably have basic autoflight modes, but no autothrust anymore which shouldn't be a problem though for any halfway competent pilot.