Sustaining Focus, mages and adepts Options

[Riley37]

It's clear that mages can use Sustaining Focus for their own buffs.
What, if anything, stops the spell?
If the mage goes unconscious, or takes a nap?

I vaguely recall text in RAW limiting Adepts bonding foci other than Weapon Foci, but I can't find it.
Adept A bonds a F4 Sustaining Focus.
Mage B casts Increase Reflexes (at F4) on Adept A.
Can they use the Focus to sustain the spell?
Does the spell still have an astral link to Mage B, does it stop if he dies?
Can Adept A de-activate the focus (to use some other focus), then re-activate it and get the spell effects again?

Could an otherwise mundane person use a Knack to bond a weapon focus?