The question to ask of any indication of infection in a carcass: is it local or generalised/systemic? This is standard inspection protocol.
A single infection site, with no other signs of ill health including emaciation, poorness etc usually means infection that has been contained in one specific area.
This abscess in this case must have been there for quite a while to have turned caseous. Plenty of opportunity for infection to spread, so as much as it looks bad, it obviously has not, so could well mean the carcass is good to go.
I would be having a second look at the carcass condition and all lymph nodes.
Sometimes there just isn’t a straightforward answer to conditions that present themselves. A judgement has to be made, which is difficult for the average stalker with little general experience.So perhaps it’s best to err on the side of caution and ‘ditch’ the carcass. On the other hand, TB is easily killed with a little heat, so cooked venison would not be infectious, however distasteful that may sound.
Here is a muntjac I recently shot (attached). Numerous sites, so it didn’t go into the food chain (but was reported - not the first time in my area). If there had been just 1 abscess or pus filled node that would have been a different call, especially as the carcass was in good condition.
It seems that post 13 above from NickJ has had experiences fitting my description - 2 nodes infected, TB. One node in a roe infected, but not TB. Of course you cannot generalise from NickJ’s isolated cases, but it does nicely show the local/generalised difference.