Probably a good question to be directed to the NZX.
Talks are said to be 'advanced' and 'exclusive'...so very far down the track despite them saying the outcome is still uncertain. Given talks have gotten this far it is fair to say that it is more likely to end in a deal than not (unless the negative media and shareholder backlash - both in terms of online forums and the fact the SP has crashed below where it was sitting even before the takeover chatter - causes the Board to make Sophie kill the deal).
But given SM is probably going to present some sort of a deal to shareholders soon...it is interesting that the shares are still allowed to trade now that you mention it.
People are dumping shares without material information being made available. And Sky can't release the terms and price until they have signed a deal with MW. So a trading halt would have certainly calmed things down and given some time for the market to digest the news, get the terms of the deal and then resume trading with a clearer head).