Not only is it possible, it might eventually be likely. The supply schedule assumes that transaction fees will be sufficient for security, but researchers have cast doubt on that assumption:
If some future generation of bitcoiners is faced with either increasing the reward or putting up with frequent large rollbacks, we can't really predict which they'll choose.
https://freedom-to-tinker.com/2016/10/21/bitcoin-is-unstable...
If some future generation of bitcoiners is faced with either increasing the reward or putting up with frequent large rollbacks, we can't really predict which they'll choose.