Might be of use to provide some context, since until I looked into it, I had no idea that Google was killing APIs, or ending active development on APIs. Source: Google blog post: "Spring cleaning for some of our APIs"
That said, nothing about that post leads me to believe feedburner will stop slurping RSS feeds even though Google is ending active development on the APU. My guess is that in most cases, abuse of the API's is frequent, and Google has decided it's not providing value to support the APIs any more. Clearly, all of this is just my opinion, and not based on any statements from Google on how feedburner's API status is related to the future of feedburner itself.
While not comments on feedburner's API, here are some official Google statements that lend support to the idea that the API's are hurting Google: "The Google Translate API has been officially deprecated as of May 26, 2011. Due to the substantial economic burden caused by extensive abuse ..." SOURCE: Google Translate API. I would also say that it is highly, highly unlikely that Google plans to kill off Google Translate itself in the future; but again, just my opinion.