I tried searching for threads related to this, but there didn't seem to be any.
Is it listed anywhere what the process of breaking a familiar's bonds would be? However, it's also very clear that this punishment is meted out at Tribunal as punishment for Lesser Crimes ("Magus X was punished by the loss of his familiar"), so clearly there's a means to break it that's not an all-season laboratory.
I'm aware that, generally speaking, such a break would result in the death of the familiar (similar to the death of its master). However, I also recall reading how familiars who have been released tend to flee and never be re-Bondable or found again, due to the trauma of the break. (This may have been written in a previous edition.)
My impression is that it'd be a Ritual at the very least, since it takes a Ritual to disenchant a magical item, which is also an all-season activity. A simple PeVi spell seems to "cheap" otherwise.
Serf's parma, but I think the bit about a familarr fleeing contact with the magus once the bonds are broken is in True Lineages, in the Guernicus section.
I don't recall there being a spell or ritual included, but if i had to make one, I would think it would be a PeVi with perhaps casting requisites of the Technique and Form used to bind the familiar.
Killing the familiar is, I think, an even harsher punishment, and if I recall there is some flavor text in that same section of TL along the lines that it is considered honorable to reject the punishment of death for the familiar and demand to be Marched instead.