Yes, you can connect both boxes by ethernet cables or as I have done, have the old Vision Box on Powerline adapters. However, My Vision Box is a BLACK Box so the Silver box may behave differently.
I have found that the Vision box works as a standard Freeview PVR and even updates its firmware are periodic intervals.
Caveat: You do this at your own risk and this configuration is NOT supported by BT so don't call them for help with it.
The silver boxes are not capable of operating standalone without BT Broadband. However, I have no idea if it will still boot properly once the YouView box goes live if still connected to broadband. I can only suggest trying it to see.