I think you have to destroy all fighters (the Valkyries) and then you get told to disengage. At the jump hole there is a little good-bye scene and when this is over the jumphole starts to work.
I guess if one of the speakers (Lord Hakkera, and another one IIRC) cannot make their speech for any reason - because they did not make it through the battle, or because your sound codecs are messed up - then jumphole won't get activated.
"Access denied" from a supposedly natural phenomenon like a jumphole, my ass. "Docking not allowed" from a friendly jumpgate or tradelane ring just because an NPC is reading something from a script, when you can normally dock even with maximum hostile ones ... These things are absolute immersion breakers, and very annoying to boot.
I wouldn't mind so much if the game did this only the first time around but it happens
every time. Keeping a 'speech heard'/'cutscene watched' flag for every speech and cutscene in the campaign would require about a couple dozen bytes at most; during subsequent passes the speeches could be treated like the other background chatter and cutscenes aborted via escape like that chats with NPCs in bars. But no ...