1. Jon said on his blog if Season 7 is not the last season then the following seasons would be like Seasons 1-4
2. Bytes: The figures tend to talk about the show in these and Hypermail. This means they are not actually dead.
3. Jon has 2 Master Chief figures, so even if one is broken in half, the other one could be used.
These are just some reasons there could be a Season 8 (I highly doubt it but I hope so.)