Hi Chris,
Welcome to the TI E2E Forums!
Our industrial products have long life spans and as far as I know the ADS1255/56 will not be going away any time soon. All of our ADS125x products are sill very popular and widely used. TI also has large factory capacities, more than our competitors do, suffice it to say we are not running out of space (...I'm glad that I don't have to store too much stuff in my cubicle!).
That said, if we were to obsolete a product we provide at least 1 year advance notice to allow for life time buys, if needed. See our quality section: http://focus.ti.com/quality/docs/gencontent.tsp?templateId=5909&navigationId=11224&contentId=5020.
I hope this information helps - If needed I can find out if there is a technical sale representative in your area that might have more information on this subject.
Best Regards,
Chris