"A pre-PEA offer could be followed up by the PEA release and that would allow for any other bid. A smart first offer buyer would have a large breakup fee though."

If a smart first offer has a breakup fee it had better be a good offer otherwise it wouldn't be accepted. Especially if ZEN has any incling of other interested parties.

I believe Inco wanted a breakup fee included in their first bid for DF but Friedland wouldn't have it, however Friedland did accept a breakup offer from the Falconbridge bid and Inco paid that fee in the end.