= CONCATENATE("= (";SUBSTITUTE(FORMULATEXT(A1);"=";"");") + (";SUBSTITUTE(FORMULATEXT(B1);"=";"");")

=CombineFormulas(A1:B1,"+")

Option Explicit
Public Function CombineFormulas(RangeToCombine As Range, Operator As String)
    'Input:  Range of cells and an operator to use when combining their formulas
    'Output: String of the combined formulas
    Dim cell As Range
    Dim s As String
    s = "="
    For Each cell In RangeToCombine.Cells
        If Len(s) > 1 Then s = s & Operator
        s = s & "(" & Mid(cell.Formula, 2, Len(cell.Formula)) & ")"
    Next
    Application.Volatile
    CombineFormulas = Evaluate(s)
End Function