USE Relationship with Switch

David_Verdon , Try using this then

DAX
Sales Value =
VAR Status_ = SELECTEDVALUE(ProjectDetails[ProjectStatus])
VAR Rev = [Revenue Actual]
VAR Fee = SUM(ProjectDetails[FeeEstimate])
VAR Result =
SWITCH(
TRUE(),
Status_ = "Closed Project",
CALCULATE(
Rev,
USERELATIONSHIP(ProjectDetails[ClosedDate], 'Date'[Date])
),
Status_ = "Live Project",
CALCULATE(
Fee - Rev,
USERELATIONSHIP(CMap_ProjectDetails_Live[WonDate], 'Date'[Date]),
REMOVEFILTERS('Date'),
USERELATIONSHIP(ProjectDetails[ClosedDate], 'Date'[Date])
),
BLANK()
)
RETURN
Result

The USERELATIONSHIP function for ClosedDate is explicitly deactivated for the "Live Project" calculation.

The problem is that variables in DAX aren't really variable, they are constants. Once they are evaluated they are never evaluated again, so trying to reevaluate them in a different context won't work. Try

Sales Value =
VAR Status_ =
    SELECTEDVALUE ( ProjectDetails[ProjectStatus] )
VAR Result =
    SWITCH (
        TRUE (),
        Status_ = "Closed Project",
            CALCULATE (
                [Revenue Actual],
                USERELATIONSHIP ( ProjectDetails[ClosedDate], 'Date'[Date] )
            ),
        Status_ = "Live Project",
            CALCULATE (
                SUM ( ProjectDetails[FeeEstimate] ) - [Revenue Actual],
                USERELATIONSHIP ( CMap_ProjectDetails_Live[WonDate], 'Date'[Date] )
            ),
        BLANK ()
    )
RETURN
    Result