We shouldn't be starting Vidal/Gomes/Paulinho anymore.
Our next 4 games before the 2nd leg against Chelsea are:
Girona (H)
Las Palmas (A)
Atletico (H)
Malaga (A)
Start him and give him around 60 minutes against Girona and Las Palmas. Then play him the full 90 against Atletico to let him feel what a high pressure, high stakes game is. 70 minutes vs Malaga and then the full 90 against Chelsea.
Our CL hopes higne on integrating him and it would be wise do it ASAP, if Valverde thinks he can get by and win the CL with our team as it is currently assembled he's out of his mind.
There's no telling whether Dembele is going to play well for us this season, but it's surely worth a shot trying to integrate him rather than playing Gomes/Paulinho/Vidal in big CL games.