"If we stay does that mean eventually adopting the Euro?"
Both the UK and Denmark secured an opt-out clause from the single currency during the signing of the Maastricht Treaty in 1992. The clause is legally binding, meaning the UK would have to agree to revoke it before the process of adopting the Euro could take place. This puts the decision entirely in Britain’s hands, regardless of the referendum result.
Since 1992 successive governments have committed to remaining out of the Euro and numerous polls have repeatedly shown that the British people are against it. In fact, 5 economic convergence criteria must be met before any country can join the Euro, of which the UK met just two at the last review in 2014, meaning that in an official sense we could not join the Euro right now even if we wanted to.
On the other hand, the EU has an increasing tradition of bending the rules, and would likely do so if the UK ever did intended to adopt the currency. The Euro crisis has revealed many of the drawbacks of the single currency, and whilst it seems as if this would lead to a revaluation of the EU project as a whole, it is more likely that deeper economic and political union will be encouraged as a solution. It is not in the Eurozone’s or the EU’s interests to have members that are not part of the single currency. In this sense the Eurozone wants all the strong economies it can get, and may encourage the UK to join the Euro in the future. Sweden is expected to join as soon as the convergence criteria are met. Certainly, new members to the EU are legally obliged to join the Euro as soon as possible, and it is extremely unlikely that any new opt-outs will occur.
A vote to remain is by no means a vote for the UK to join the Euro, and whilst we cannot be certain, it is very unlikely that this would happen. If we vote to remain in the EU and there is a future movement for the UK to join the Euro, it would likely be ignited within Europe rather than domestically and would surely be met with reluctance from a UK which is trying to battle further EU integration even now. If such a movement did rear its head, and if current sentiment continues, it would stand as much chance of sparking another referendum on EU membership as one on adoption of the Euro.