Tim,
You might want to consider changing your statuses to better reflect the process you described.
Instead of "Dead" for a lead that isn't ready, why not say "Nurturing"? Then your system drops that lead into a predefined nurture. If you setup a Reason Code or something else, Marketo can then choose "9 Month Nurture" or something.
To me, Dead or Trash or Unqualified means don't bother ever again. I like Clinton's options for negative states.
Another option is to setup a task to call in 6 months or 5 months so you're in the running for the sale.
Still another option is to automate the task creation with a combination of change Lead Status value and Reason code.
And the option Marketo loves you to use is to set the Lead to Nurture and then have the lead score bubble the person up after enough activity.