The short answer is that teleportation is an advanced skill and there's hundreds of mages.
TRISS may not be in any danger but everyone else is.
True. Most of the mages don't even seem to be Sorcerers/esses proper, just alchemists, petty practitioners etc. etc.
The short answer is that teleportation is an advanced skill and there's hundreds of mages.
TRISS may not be in any danger but everyone else is.
Well, megascope is just a machine. It requires skill to build it, but operation would be not very difficult. Triss teleported herself and Letho with no problems. Sure, she should know coordinates, but it was very easy to send a servant to Kovir long time ago, when the trouble started, to consult with Carduin or some other capable mage, and bring them a set of coordinates for safe teleportation. Sure beats all this sneaking, fighting, dungeon crawling, etc. Triss managed to save only about 30 mages anyway, and on a pretty bad ship. With megascope she could have done it in half a day.
I stopped to pay attention to minor inconsistencies long time ago. I really like the game, like really-really like it, even the political part I find quite great, even though I have to adjust or even invent a sizable share of it, so I am not really into any nit-picking.
But we know teleportation is not entirely safe. 1 in 100 trips ends very badly.
There's also mage arrogance to deal with.
How many mages didn't take the Eternal Fire seriously until everything went to hell?
Isn't Triss mansion newly sacked?
Yes it is, however Gerald tells Sigi during dialogue that the mage persecution started "months ago".
Sigi replies it wasn't "on this scale" though.
It's unclear how long has Triss been working on her escape plan.
They may have found themselves trapped ex abrupto more or less in the last few weeks
The simplest way to deal with it is to explain in-game that there are magical blockades around Novigrad that prevent from teleporting outside of Novigrad area. They can use magic in the city (which may be tracked by witch-hunters as we now track active cell-phones), but no teleportation would be possible, even with a megascope. Radovid kept Novigrad a free city for a long time for all mages on the run to come there, and later shut the trap in order to mop up all survivors. He wouldn't leave any of them an easy way out. It would be quite in his character.
CUT
Tbh though they don't even need any of this, they can just swim their way out at night.
Still, it made for a dramatic and good moment, so I'll suspend my disbelief.
The issue is not leaving the physical boundaries of the city, it's leaving Radovid (and for some, surely even Nilfgaardian)controlled territory.
Witchhunters + Sacred Fire patrols/agents are operative all round the map with the exception of Skellige and KM, proof of that is during the 2nd Pellar quest where some witchhunters show up, and that's in Velen.
I suppose you have a point, yet there were some scoiatel units in the woods and nobody was bothering them (do they even care about them anymore, Roche certainly didn't).
In any case plenty of places to hide in the forests before the ship is ready instead of being in the center of the hunters power.
Also regarding that quest, it was a ritual that was not exactly secret, so many villagers were present that it stands to reason that word got out and they got there on purpose, not that they were patrolling and just happened to run across them. Even if we admit the possibility that they were cough by accident, the island WAS haunted so maybe the hunters were dispatched to try to investigate the curse.