Hi Lisa,
I use a rolling contract and it works well for me, any contract will have 2 methods of termination, cause and convenience. I would assume the 90 day notice period will be for convenience, typically if the customer is not happy he will have to serve notice on the existing contractor to improve and maintain the service or lose the contract typically I would expect the improvement to occur within 7 days and the termination notice to be 30 days. If the customer has complained and these complaints are in writing termiation for cause will be streight forward.
It is difficult to advise but the rolling 12 month term may refer to changes in price. The best advise is to speak to the client and ask him what you need to do to motivate him to change contractor, just remember your commitments under TUPE especially if the current employees have been in place for long periods.
Good luck, Geoff