What happens if a transaction containing an extremely large numbers of outputs and a very large mixin exceeds the current dynamic blocksize limit?
If simplewallet is creating this tranasction (or any other wallet software using proper protocols), the transaction would be broken into multiple transactions that would be more compatible with the current dynamic blocksize limit. If a raw transaction gets pushed to the daemon, or is otherwise created and pushed to the daemon, then the following question is valid.
Will the daemon reject the transaction?
AFAIK, the daemon will only reject a transaction if it does not meet consensus rules. So, if, for some reason, a larger than blocksize transaction was created and all consensus rules were met, it would get relayed and sit in mempools until it expires.