
Thanks for all your good wishes, they helped a lot.
Ignatz got through the operation and is now back home. The vet was right and it turned out to be a tumor, which of course wasn't what I had hoped for, not just because tumors may likely come back, but because it was much harder to operate, especially as according to the vet the tumor was very connected to the surrounding tissue so the operation was very bloody. Ignatz still seems quite lethargic and unwell, which I guess makes sense after loosing blood. He also looks rather pitiful because of the shaved fur around his throat, and the rest of his coat looks bedraggled as if he hasn't bothered to groom yet.
But the vet said he woke from the anesthesia okay, and he that he has eaten some (though I could see that the rodent food mix they had wasn't the kind he likes), and now that he's home I've seen him eat some banana before retreating into his house as well. The vet also told me that he actually tried to escape from the box this afternoon. They had to keep him in his smallish transport box I brought him in, because they didn't have room on their station in one of their regular cages, and I didn't know he learned how to open it (he never managed with me nearby) but he apparently succeeded there and they had to tape it shut on top of the latch. So I take that as a good sign of initiative and recovery, that he tried to stage jailbreaks.
I still have to keep him separate from Emil, so that the stitches on his throat are left alone and he can recover, because obviously another rat could get easier at them, as Ignatz can only reach them with his paws, not gnaw on them with teeth, though the vet said he was fairly good with them so far, and hasn't disturbed the wound. And of course he smells very strange much more so than after a regular vet visit, so while my two usually don't tussle much any more, Emil might react to that as well, and I've divided their cage for now.
This is one of the times I'm really glad I spend quite a bit of money on a sensible rat cage, because I didn't have to set up a separate, unfamiliar recovery cage, but could just put in a premade divider to block some of their levels from each other, and he can recover in a familiar smelling place, and Emil just has the inconvenience that the upper area will be blocked to him, but remains in the cage he knows as well.
I have to bring Ignatz in again tomorrow for a wound check, but for now he's curled up in his house and as okay as can be expected I guess, after after anesthesia, removal of a large tumor, and loosing quite a bit of blood. But I hope he'll recover, and that having had this operation will turn out the right choice that will buy him the most time and best quality of life possible.
ETA: Emil just discovered that I cut off much of his cage from him and seems very cross about that. He now checked whether the unwanted divider was still there no less than three time in the last ten minutes: Going up the stairs where normally there is a hole and pushing his nose against the metal wire mesh now blocking his access to the upstairs levels (he got the lower levels so he can get outside easily, whereas Ignatz for obvious reasons doesn't feel like playing so he got upstairs).