I think that despite Messi's desire to come here and our readiness and preparation to do the deal, people will have to be patient and I can see this rumbling on (and there is a danger to that as well as we know he could have a change of heart and that would surprise no one)
Barca board and management are going to make this drag on - they will clearly say there is a year left on his contract and unless the buy out clause is met he stays (and no one is going to meet that, not even us). They could even refuse to negotiate with us. If they do negotiate then that will also be a protracted affair as they will be pissed off that it is happening
All the while this is happening Messi will have to train with Barca (We know he is already intending on doing this) and thats when there is a slight danger he starts to feel the desire to stay.
Hopefully we can get this over the line but I feel there is a lot of politics to sort through and the media will also do their best to muddy the waters for everyone.