If you happen to be in the planar vortex when the game crashes the main quest become broken and you cannot continue.
Tried to make it work:
1) after crash start game, login back onto character in planar vortex - no enemies there to kill the planar vortex entirely empty, cannot progress further
2) go back to entrance, leave the planar vortex and come back again - does not help, no changes
3) logout to character chooser and the back into the character (while the character inside planar vortex) - does not help, no changes
4) port to Vvardenfel (Vivec City wayshrine), logout to character chooser (and planed to log in from there) - but game crashes on logout
5) start game from launcher and login onto character after the second crash - screen now spinning (on Vivec wayshrine)
6) quit game, exit launcher, start launcher, start game, login onto character in Vivec (which not spinning now), port to the last wayshrine in Coldharbor, run back to planar vortex - on entry quest reset to the beginning so I do the part I already done until the crash
7) reaching the site where the crash happened - the quest still broken and still no enemies there to kill
8) kinda giving up, going for a drink and leaving the character there - after a few minute the enemies which supposed to wait for the character suddenly spawn out of the blue and surprise, I can actually finish the quest
, please, you really really need to fix the stability of the game because the above is just not acceptable.