The rebate could only be withdrawn if the UK agreed to it as changes to rebate required unanimity of the European Council. The rebate is part of the Multiannual Financial Framework -
http://www.bbc.co.uk/news/uk-politic...endum-36085281
It is a very good point that the leave campaign was in no position to make promises as it wasn’t the government. I didn’t have a great deal of time for David Cameron before the referendum but I did admire the fact he resigned as he was a supporter of remaining in the EU