I have the original Calebais supplement. I've run it twice in one saga (they needed a return trip years later, after the necessary preparations) and it became the base to form a new covenant in a spin-off saga. The original story has even repeated itself in the spin-off saga, during a very odd episode in anearby high level regio. This is put very short. The somewhat longer version goes:
First run of the adventure, was with relatively young magi and relatively inexperienced ars players (though already at that time veteran role players). Both the ghosts and the Hrool gave the magi problems, as did simple traps, difficult terrain, cave-ins and floods, along with the earth elemental in the floor of one of the labs. They managed to interact with quite a few ghosts, and give many of them peace of mind and final rest. I can't remember if they helped some of ther Hrool to leave and set up their tribe outside this time, or if it was in the next. I do believe the Hrool split up into two factions, and one of them stayed behind. Also, I don't remember if they managed to find the Bell and haul it home this time or the second. Pitsdim gave them a lot of bother, and while unable to fight him, they had to avoid him. Because they only solved part of the ghosts'unfinished business, he remained unchecked. In the end, they went home to lick their wounds. It was a partial succes, they managed to get quite a bit of swag, and they learned a lot. They publizied their findings, and ended up discrediting the surviving magus (whazzis name?), who had claimed it was demons, when in relaity it was pride, arrogance and human frailties that ruined Calebais.
A good deal of gam-years later, the troupe opted for another go. This time, they came beetter prepared, they were more experienced, and some changes in teh roster had happened. Among others, a new player had made a ghost-specialist, plus there were some apprentices. As mantioned above, I can't recall whether the Ball and the Hrool happened this time.
A lot more ghosts were resolved, and in the end even Pitsdim was confronted. His familiar played some part, I believe they managed to use it to get contact with him, and make him realize certaina spects which his amdness had prevented. A tragic end of course, but it still stopped him. j Little more loot was found this time. The flooded levels were investigated somewhat, the collapsed levels weren't. Because they were completely caved in.
Some years IRL later, we started a new saga, with a few old and some new players. It was set after the end of the first, but in Norandy Tribunal (the first was in Stonehenge). This way, we used all events and people previously defined. This new saga was about a group of young magi wanting to settle Calebais again. We had a lot of stories to begin with, regarding what was left. We redefined the location of Calebais to better fit the new saga, since it had bever been very accurately put on a map. The colapsed levels were re-defioned as just caved in, and were cleared. We drew additional maps of these missing levels, and put the labs of all the resident magi from back them on. The saga lasted 30 game-years and several RL years. In the end, the magi had built a large stone manor on top of the hil, as the front for the covenant (as the area becase less wild and was partially retaken by mundanes), with the "well" of calebais in one courtyard. The Calebais advanture served as backdrop, since the ghosts and whatnot were already resolved, except bits and snipets in the start of the saga.
Some time during the saga, a very odd event reagrding a neaby high-level regio trapped all the magi of the saga inside. When they returned to their home, it was the old calebais. It turned out the last hours of Calebais happened again and again. Using character knowledge of what had happened during the old saga's adventure there (these old magi had published most if not all of their findings), they did a quick re-play of interaction with ghosts, to resolve the ciscis. It was a good advenyure, even this time. It was still new for some players, and the old ones could only remember bits.