Well, technically you have all the customer data in your gateway's info manager (like Authorize.net's CIM), but it would still be a real bitch to take that and do anything useful with it. Plus, the clock is ticking on your 30 days to get it migrated to your new setup.
Honestly, I haven't looked closely at the raw A.net API. I heard about Chargify, pricing looked good, and it fit my model. Basically, I wanted someone else to deal with dunning, expired cards, running the periodic charges, etc, etc.