While there are ways as others have said to fake a beheading, as far as I can tell, there are very few ways to survive an actual successful beheading.
The most likely to potentially survive are the Tzmisce and the Tremere but only one who is very, very skilled and clever and has had prior time to prepare for the event of a beheading. Which I suppose the VtM:B sire might well have had.
This is how it could be done:
Vicissitude: A Tzmisce with enough skill, could probably move their brain to not actually being where you would expect it to be, with how much mastery they have over their own bodies. They can also inflict this on others - for instance, Malgorzata was a non-Tzmisce kindred that found herself hideously tortured and warped by them. Other vampires eventually discovered her and tried to mercy kill her, but had a difficulty finding where her actual brain was to chop off.
I imagine a more subtle version of this could be employed too than full-scale obvious warping.
This would not apply to the protagonist's sire however, as they cannot be Tzmisce: unless you want to believe that the to-be-sire pulled a very dark favour some point somewhere and had someone else do it for them.
Tremere ritual: A tremere regent/primogen named Hannah, canonically survived an assassination attempt by "simply" putting her soul elsewhere from the body which was destroyed.
Later, it is revealed that Hannah actually survived the assassination attempt by migrating her spirit into a statue
Hannah was 7th generation too: and as the player's sire must have been 7th as well (by virtue of their childe being 8th), then there is more of a chance of them being powerful enough to also successfully pull something like this off.
There's also some Tremere who even pull a "grand theft me" and body snatch somebody - although that has been extremely rare as far as I can tell.
The only examples I know of off the top of my head - although others may feel free to correct me - are 4th generation kindred hijacking other vampires in their clan...but if a 7th gen can put their soul in a statue they might be able to perhaps hijack a weak-willed mortal or something along those lines. Perhaps a pre-prepared ghoul if it requires a bloodline connection.
Although I have to admit there's little specific information on that, at least that I've been able to find anyway, unfortunately.