First of all I think if you make the decision that Romero plays EL, you can not just take that away from him when things start to become interesting. It shows a complete lack of trust to your player and I don't think he will want to remain at a club that has a complete lack of trust in him.
Secondly, Imagine dropping Romero for Dave and then Dave playing a really bad game and costing us the EL. Where do you go from there ?
Unless Jose feels that Romero is a liability at the back and will cost us points, I don't think he should just replace him with DDG because the stakes are higher for the club. Not unless a situation like this has been anticipated and discussed with Romero well beforehand.