No, the money on the SideKick Card does not expire. As long as you have an active SideKick account and card, the money may be spent or withdrawn from the ATM.
It's important to say that after a 180-days period as a dormant account, SideKick will have a monthly administrative requirement of CAD 2.50 from there, until the balance is used or terminated.
For an active account, there is no fee.