This is admittedly an edge case, but hey, it is important.

What can happen:

1) A Customer accepts an Estimate

2) The line items accepted become 'unscheduled work'

3) The work is scheduled and the client is notified.

4) The client calls prior to the work being done and asks to decline the estimate.

5) Someone is able to change the estimate status to 'declined' despite the work be scheduled or invoiced already.

Suggestion:

If the Estimate has been invoiced OR scheduled from, the action to edit the Estimate should prompt a dialogue box "This Estimate has been scheduled from. Are you sure you want to modify it? Jobs that have been scheduled will remain on the schedule."

Thanks,

Brian Rand