Seriously Valencia have been underperforming this season. Just look at their dismal results during the start of the season is enough to make you think it's gonna be a long and hard battle for them in La Liga as well as UCL.
But kudos to them for managing to turnaround their season a little by winning the Copa Del Rey. IMO, lifting a cup when everything isn't going their way is certainly a good enough reason to be cheerful albeit for a while.
Regarding the sacking of their manager, i think it's inevitable. I guess the the board can't tolerate the inconsistencies.