There is a large structural member that goes up and over the passenger compartment above the seat backrests.
The actual fiberglass roof panel that fits in the gap over the passenger has no structure to it that would give it rigidity in the even of a rollover, however. The targa design should satisfy a lot of track requirements which would prevent use of a convertable without a rollbar. However, at a certain level of intensity and competition, a rollbar would be a no brainer anyway just as it would be in any other steel roof car.
