In my personal experience, a "real vent" on top of the roof (cupola, turbine, etc) is far more effective than continuous ridge vent, and I will in fact be retrofitting a cupola onto a roof with continuous ridge vent for exactly that reason. The space feels nearly unvented, despite "being vented" as the air movement through the ridge vent (with plenty of venting at the eaves) is pathetic.
What you have there appears to be a "mushroom fan vent" rather than a turbine vent (i.e it only really moves air when powered up, while a turbine vent as I understand the term vents passively all the time and more actively whenever the wind blows.) That can be useful for increasing air movement in the space when needed, and should not be particularly prone to leak if it's in good shape. It would not meet code requiring passive ventilation, though.
I would strongly suggest reading the actual code applicable to your local area to see what it actually calls for, rather than accepting that it specifies "ridge vent" if, in fact, it simply requires passive vents but does not specify how that is to be done (which would be more likely, in my experience.)