I'd be cool with it if they sell Neto and promote Pena. Neto's salary is crazy for a 2nd GK. In the end the 2nd GK will play less than 10 games if MAtS doesn't have any complications after his injury. It's a risk as Pena lacks experience, but the club should take the risk given current circumstances. Time to give homegrown players more chances rather than spending money for a 2nd GK, even though Aitor Fernandez is a good one.
That being said, the club needs to get rid of Neto first which won't be easy.