Valverde's too close in GC to let go, he could have ended up staying away, especially with team mates around him. Froome made the right call to go after him, though it is also playing into Valverde's hands as Froome hasn't got any help to chase down.
But Evans has managed to claw himself back, so Porte might be able to as well. I do think Froome will be vulnerable if he goes into the next climbs without any of his team there, and Porte's the only one capable of getting back to him. Sky's lack of strength in depth is really showing here - last year this wouldn't have happened. But Froome is capable of dealing with it if he doesn't have to over-exert himself doing too many chases too early, and he's a decent descender so he can afford to let rivals get up to about a minute up the road, though obviously he won't want to do that at all.
I expect Valverde will try again, and maybe Contador's saving himself for the final climb...
Have to say though, looks as if Sky have made a bad team selection error in not having enough decent climbers - there are far too many mountain stages left for them to be able to cope with this type of stage repeatedly. Hopefully the rest day will help Porte and Kennaugh, but they can't help Froome defend the jersey alone. Boasson Hagen is good for the flat stages, but most of the rest of Sky have been pretty anonymous so far, and their lack of depth on these mountain stages is startlingly poor.