Not according to our manager, otherwise why sanction him leaving? Unless you claim to know better than the manager which players are useful or not?
Sanchez wasn't keen on staying
Ange probably thought playing one game a week, we might have one CB out very unlikely two out at same time.
We have Davies who plays LCB for Wales, Dier and possibly Phillips available to play CB plus Royal at a stretch.
Its low risk to let Sanchez leave after window closes and not get in a replacement until January - so no drama if he leaves