A second referendum won't happen but if it does I don't think that it could legitimately include the possibility of staying in the EU as issue was already voted on. The only question that remains, is how do you leave the EU. The fundamental problem with having a referendum on this, is educating the population on the different options and the consequences thereof. Recall how surprisingly difficult the referendum exercise was when it concerned a simple in or out question. The referendum will be hard to explain that it would run counter to what referendums are to be used for - indicating the public's position clear cut issues - which Brexit is anything but.
Let's say that Parliament decided to go ahead with a People's Vote (which again excludes the UKOTs because it would seem that they aren't considered people by many MPs), they could not have it between now and the 29th of March 2019 as that period is too short to figure out the manner in which the options are set out and explain a very complicated set of questions to the electorate. Therefore, Parliament would have to amend the Withdrawal law so as to extend Article 50. Regardless of the outcome of that referendum, the UK would be liable to pay even more than it does now, in a time when it needs to continue cutting debt.
It is for these reasons that I believe a People's Vote is totally and utterly impractical.