737ng can be flown without FMS and I did it a copule of years ago(Both FMS failure at an airport with no maintance cover). You just set the vspeed and N1 limit using the knobs instead. Regarding the RNAV, Airports should have contingency procedures in case an aircraft lose its rnav capability(eg:omnidirectional departure or radio aids to hold in case of radio failure). In Salzburg the airways bring you directly over the VOR and from there you can star your procedure.