Article 50 not the only option
Greenland did not use article 50 when it left! There are other options like article 48 and also Vienna treaty options and Royal prerogative using new Orders in Council which will be deemed primary legislation over riding old laws. Orders in Council have been used in past and called valid by supreme court in the Chagos case where the govt set aside court orders regarding Chagos island's. Or Parliament could just issue new law breaded on referendum result annulling previous law entering EU which would unilaterally strike this down.
The government spent £7 million sending leaflets to every home and on it it clearly says the referendum decision is for the people and the govt will implement what ever the people decide.
Zoopla allegedly is one of the companies finding the legal action. I guess one of the reasons for them is financial reasons to delay knowing property situation now see https://twitter.com/zerohedge/status/750045373582966784 and see the article in question http://www.zerohedge.com/news/2016-07-04/bear-stearns-20-uks-largest-property-fund-halts-redemptions-fears-vicious-circle