This is a good question.
AFAICS, there is no general rule, what becomes of an AC to a person, if that person dies. Does it cease to be an AC, become an AC to the body or to the spirit (provided no Church burial or such took place)?
Or what happens to an AC to some thing, if that thing is later taken apart. So does your AC to a wagon become an AC to the box, a wheel, the drawbar, to all - or does it just cease to be an AC?
We know, that at the death of a maga the link to her familiar decays (ArM5 p.105 The Familiar in Play), reducing the familiar to a pathetic, devastated state - so the familiar is likely no longer an AC to its dead mistress's body and/or spirit.
If a magus with the Minor Hermetic Virtue Harnessed Magic (HoH:TL p.105) dies, all his spells and magic items 'sputter out' - as he was still connected to them.
The connection of the Rune Caster to his Rune is both ways (HMRE p.125), just like that of the familiar to its mistress: so I might rule that the Runes 'sputter out' at the caster's death as well. It could save the SG some head aches.