[Vedran]

Six: Whan Jan joins, a timer is set to fifteen days. You joined him with Ctrl+Q and skipped that part.
Anyway, he should have had something to say to you, had the game been patched at the time?

Calaethis:
1) "the wrong dialogue entry" is "Good riddance, gnome..." or "I'm afraid we haven't got time..."? If former, he's gone for good. If latter, he should go to his home (have you checked all the floors?).

2) How to get Jan back?
Save the game (in the case we ruin the game completely).
Type the aforementioned command: CLUAConsole:CreateCreature("JAN12") (Exxon is right. JAN15 is from ToB).
Now, there are some variables that need to be adjusted. Jan would be a brand new Jan, his dialog and quest should be reset. You have two options now:
2a)If you use Shadowkeeper, save the game in a different slot, exit and open it with SK. Find variables:
JanMove
TalkedToJan
JanLissaPlot
And set them to 0
It may be tricky to find them, as I believe those are not sorted alphabetically. If some of those is not present, create it.
2b)The other option is setting those via the debug console:
CLUAConsole:SetGlobal("JanMove","GLOBAL",0)
CLUAConsole:SetGlobal("TalkedToJan","LOCALS",0)
CLUAConsole:SetGlobal("JanLissaPlot","GLOBAL",0)
Now talk to him and pray...