Yes the dog can still bloat. Gastroplexy does not stop bloat, it helps prevent torsion, but is not a 100% fix.
A friend's wolfhound bloated after having had gastroplexy following a previous bloat incident. During the second bloat incident he popped the stomach tack and died.
This is not the norm, but can happen.
When I had my Wolfhound's stomach tacked she was on strict bed rest for 3 weeks -- my vet said this is CRITICAL during recovery from gastroplexy since they can easily pop the tack during the first few weeks, even jumping up onto furniture will do it.
I would not hesitate to do it again if I had the abdomen open on one of my dogs. It's an added preventative. I would not open a dog just to do it though, unless there is a strong family history of bloat.