Yep, that did the trick. Dramath was back after I reset, and I was able to defeat Vaylin without too much trouble. Thanks very much for help.

Here is a problem that I have not seen described elsewhere in this thread (apologies if I overlooked it): On my first time trying this battle, I had Lord Dramath with me from the holocron and had him set to heal, and the fight against Vaylin's and Arcann's spirits was going OK until I died from getting knocked over the edge by that knockback of Vaylin's. I figured, no problem, I will just have another go at it later. I had to log off right then for IRL reason and come back online later, but that shouldn't make a difference. But here I am later in the day, trying the Vaylin+Arcann spirit battle again, and this time I have no companion. Dramath is listed in my Companions list but is shown as not summonable "due to story reasons". Is there anything I can do to get him back - just for the Vaylin+Arcann battle, of course - or am I just doomed to handle this battle on my own? Supplementary info in case it matters: Level 70 Commando on the Shadowlands server.