One of the things you can do is in your flow steps for that campaign is to do a check on the existing lead and if the status is Dead, change to open (or whatever your default is) and it will be resurrected - if you just synch it will keep whatever is there.
We use multiple forms and if we have a negative state (Disqualified, Bad Data, Unresponsive, etc) we will update to the handoff state (open) if it is progressing due to another interest (working, contacted, etc) we leave as is so as to not disrupt, but they will see the new activity on the individual.
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.