Barca is weird because so many chances are created by Messi's genius, he fashions so many chances for himself by dribbling that Romario (or literally anybody, ever) couldn't.
But at the same time, that's a product of the system they play, he doesn't lead the line and play on the shoulder the way others would - so this actually necessitates creating harder chances. If Romario was playing you assume it would be a much more normal approach to attacking.
All in all I think it's hard to predict how many he would score, initially I think it would be a feck load and similar to Messi, but Barca would need to play a different style IMO which is why I would be hesitant making that assumption.