The two Romulan Warbirds would have destroyed the Enterprise (or severely crippled it anyways). Any survivors would have been picked up by the Romulans then tortured and probably executed afterward.
I'm sure that Romulans would have said long range sensors picked up the "rogue" Federation starship in the Neutral Zone on it's way to invade their territory. The two Warbirds intercepted Enterprise in TNZ and were forced to destroy it. Considering everybody that was abord the Enterprise was either dead or in the process of being tortured, who would say otherwise?