Meandering

I lost my way. I tried to get ahead of the game a little and actually outline this section of the adventure, in order to better be able to fill in the details and keep some level of continuity. Unfortunately, I forgot my script as soon as I'd written it. I plowed on as if the outline were the adventures, and not the preamble to adventure.
The fortress is meant to serve as a central figure in this stage of the adventure for multiple encounters before the action once again shifts to moving upriver. The interaction with the emissary and the excursion to the stone giants to recover the axe was the first of these. Getting kidnapped and escaping from the kobolds was the second of these encounters. The party should be encouraged to return to the fortress to rest, recover, regroup - take your pick.
I like the idea yesterday's session ended with, of having something storm the fortress and overrun it, destroying it in the process. This will destroy the party's refuge and force them to continue their journey. But, the big adventure in the area was meant to focus on locating and destroying a young white dragon in its lair. That slipped my mind until today.
The build up to that was to involve scouting out the valley, tracking wolves and such up into the hills, and then attacking the lair once its location was finally determined. This is where the party should be next.
Following the escape from the kobolds, the party should need to return to the fortress to gain a long rest. Perhaps adding one or two aspects to the pursuit by kobolds should be added to encourage return to the fortress. One option would be that they left some of their belongings there to return for. Another might be to increase the number and strength of any pursuers in order to inflict greater damage and threat to the party as they escape so they feel compelled to seek shelter and recover fully. A third option would be to add a feature or magic to the cultist's shrine that has healing properties so they feel encouraged to return for healing. Perhaps adding some lycanthropes to the pursuit or an attack so there is a curse that needs to be removed by accessing the power of the shrine.
I'd be inclined to add most, if not all, of these elements.
Once the party is safely ensconced in the fortress, I would allow them the security of a long rest and the ability to fully heal or recover from a curse. I think the natural extension of this leg of the story is that the pursuers realize the characters have reached a point of relative safety and withdraw. They return to their warrens, then send out runners to recruit many more kobolds and larger, more dangerous allies, to return to the fortress in force. This can be the destructive army that overruns the complex and destroys it, forcing the party to flee.
That attack will come in 7-10 days, giving them time to track down and defeat the dragon before continuing upriver. Tomorrow, I'll get back on track, detailing some of the searches and encounters found looking for the dragon, then we'll get to the lair and beast itself, before dealing with the destructive assault. Tomorrow, I run a game, so tonight I'll sleep and prepare for that in the morning. Then we'll give this more proper attention.