The option were
1) Remain a member of the European Union
2) Leave the European Union
there was no leave but with loads of conditions, it was leave full stop. Lock stock and barrel.
Not....really...
For one thing it wasn't legally binding in law or anything, it was an opinion poll. It was up to the Government of the day to;-
A) Act upon it or ignore the result entirely
(but that would open the door for eurosceptic MPs to likely win a swathe of seats in Parliament.)
B) Decide how they wanted to have continued relations with the EU afterwards; either 100% leave, or leaving with some associations, as per agreement.
I, for one, would have liked to have seen our Government negotiate for continued access to the Single Market to continue tarriff free trade, continued Freedom of Movement of Labour
(because we have never had the full "freedom of movement" as we were never in the Schengen agreement) an end to the Customs Union
(which prevented the UK doing independent deals with other nations free of EU restrictions and interference, the India Deal and our joining of CPTPP as examples) and an end to our EU budget contributions on the scale that it was.
This was all possible, the EU themselves even outlined examples as to how such a relationship could be achieved, but the moment Teresa May came up with the
'Brexit Means Brexit' nonsense and the Remainers collectively lost their civilised minds as a result, there was only one way it was going to go.
Note: The only real rubber stamp for the 'Brexit' we have was giving Boris Johnson's Conservative Government and Cabinet a majority in the HoP, which he got in 2019. He got 'his' version of 'brexit' done.