A long-running battle to win the largest bank takeover in European history is entering its final stages.

The highest court in the Netherlands has ruled that the Dutch bank ABN Amro can go ahead with the sale of LaSalle Bank of Chicago, clearing the way for Barclays of Britain to win ABN Amro in an $87 billion deal.

The LaSalle sale, to Bank of America for $21 billion, has been seen as crucial to ABN Amro’s efforts to thwart a rival, $96 billion bid from a consortium led by the Royal Bank of Scotland.

The question now is what Royal Bank of Scotland will do next. Some expect the group will quickly come up with a revised offer that takes LaSalle out of a deal.

``It is inevitable that the Royal Bank consortium will now bid for ABN ex LaSalle,'' Len Riddell, fund manager at Martin Currie Ltd., told Bloomberg News. ``The managements of the three banks have put too much effort into this deal to simply walk away.''

There may be an alternative strategy. The Financial Times’ Alphaville blog points to a report from Dresdner Kleinwort earlier in the week that addressed what would happen if the court ruled for ABN Amro and allowed the LaSalle sale. The report suggested that the consortium could just waive the conditions of the original proposed offer – and stick to its bid price of 38.4 euros a share, but make it all cash instead of cash and stock. That would put Barclays, with its offer of much lesser value, under significant pressure, the report notes. And Alphaville adds that this report had been emailed by public relations representatives acting on behalf of the Royal Bank of Scotland consortium, suggesting that it is an option under active consideration.

Patrick Hosking of the Times of London, however, says that with LaSalle off the table, ABN Amro looks a lot less attractive to Royal Bank of Scotland. “Without it, R.B.S. stands to pick up a second-division wholesale bank,” he writes.

The ruling by the Dutch Supreme Court on Friday overturned a lower court decision that said that under Dutch law, ABN Amro shareholders had to vote on a sale of LaSalle. 

If Barclays succeeds, the combined bank would be the sixth largest in the world, with operations in Europe, Asia and Latin America, as well as Barclays’ strong capital markets business in London and New York.