Private Function fFlipPC(ByRef InPointColl As IPointCollection) As IPointCollection
    Dim pOutPC As IPointCollection
    Dim cnt As Long

    pOutPC = New Path
    'pOutPc.RemovePoints 0, InPointColl.PointCount - 1

    For cnt = InPointColl.PointCount - 1 To 0 Step -1
        pOutPC.AddPoint(InPointColl.Point(cnt))
    Next cnt
    fFlipPC = pOutPC
End Function
Private Function fJoinPC(ByRef FirstPointColl As IPointCollection, ByRef SecondPointColl As IPointCollection) As IPointCollection
    Dim pOutPC As IPointCollection
    Dim cnt As Long

    pOutPC = FirstPointColl
    For cnt = 1 To SecondPointColl.PointCount - 1
        pOutPC.AddPoint(SecondPointColl.Point(cnt))
    Next cnt
    fJoinPC = pOutPC
End Function
Private Sub UnsplitAllLayer0()
    Dim pLayer As ILayer = My.ArcMap.Document.FocusMap.Layer(0)
    If Not (TypeOf pLayer Is IFeatureLayer) Then Exit Sub ' must be a feature layer

    Dim pFtLayer As IFeatureLayer = CType(pLayer, IFeatureLayer)
    ' step one: find the likely locations..
    Dim pLikelyLocations As IMultipoint = New MultipointClass()
    Dim pLikelyPC As IPointCollection = CType(pLikelyLocations, IPointCollection)

    ' get a cursor on all your lines
    Dim pFtCur As IFeatureCursor = pFtLayer.Search(Nothing, True)
    Dim pFeat As IFeature = pFtCur.NextFeature()

    Dim pTopOp As ITopologicalOperator
    Dim pBoundary As IGeometry
    Dim pBoundaryPC As IPointCollection
    Dim pSpatFlt As ISpatialFilter = New SpatialFilterClass()
    pSpatFlt.SpatialRel = esriSpatialRelEnum.esriSpatialRelIntersects
    Dim pSrchGeom As IGeometry

    Do Until pFeat Is Nothing
        pTopOp = pFeat.ShapeCopy
        pBoundary = pTopOp.Boundary ' both ends
        pBoundaryPC = CType(pBoundary, IPointCollection)

        For pPntCnt As Integer = 0 To pBoundaryPC.PointCount - 1
            pTopOp = pBoundaryPC.Point(pPntCnt)
            pSpatFlt.Geometry = pTopOp.Buffer(0.01) ' use a suitable small number here
            If pFtLayer.FeatureClass.FeatureCount(pSpatFlt) = 2 Then
                pLikelyPC.AddPoint(pBoundaryPC.Point(pPntCnt)) ' store this point to go back later
                ' add some code here for checking attributes
                ' if that's important to your network
            End If
        Next

        pFeat = pFtCur.NextFeature() ' go next..
    Loop

    Dim pEd As IEditor = pApplication.FindExtensionByName("ESRI Object Editor") 'http://help.arcgis.com/en/sdk/10.0/arcobjects_net/conceptualhelp/index.html#//0001000004nn000000
    pEd.StartOperation()

    ' now go through the likely locations and dissolve
    For pLikelyCnt As Integer = 0 To pLikelyPC.PointCount - 1
        pTopOp = pLikelyPC.Point(pLikelyCnt)
        pSpatFlt.Geometry = pTopOp.Buffer(0.01) ' use a suitable small number here
        Dim pUpCur As IFeatureCursor = pFtLayer.FeatureClass.Update(pSpatFlt, False) ' must be false here
        Dim pFtInto As IFeature = pUpCur.NextFeature() ' the one that will get the shape
        Dim pFtRem As IFeature = pUpCur.NextFeature()    ' the one that will be removed

        Dim pIntoPC As IPointCollection = pFtInto.ShapeCopy
        Dim pRemPC As IPointCollection = pFtRem.ShapeCopy

        ' there are 4 possibilites for line orientation:
        Dim pProxOp As IProximityOperator = pIntoPC.Point(0) ' start point
        Dim pFromFromDist = pProxOp.ReturnDistance(pRemPC.Point(0)) 'distance start-start
        Dim pFromToDist = pProxOp.ReturnDistance(pRemPC.Point(pRemPC.PointCount - 1))   ' distance start-end
        pProxOp = pIntoPC.Point(pIntoPC.PointCount - 1)
        Dim pToFromDist = pProxOp.ReturnDistance(pRemPC.Point(0))   'distance end-start
        Dim pToToDist = pProxOp.ReturnDistance(pRemPC.Point(pRemPC.PointCount - 1)) ' distance end-end

        Dim pOutPolyLine As IGeometryCollection = New PolylineClass()
        Dim pOutPath As IPointCollection = New PathClass()
        If pToFromDist < 0.01 Then
            ' simplest case just extend
            pOutPath.AddPointCollection(fJoinPC(pIntoPC, pRemPC))
        ElseIf pFromFromDist < 0.01 Then
            ' flip first then join
            pOutPath.AddPointCollection(fJoinPC(fFlipPC(pRemPC), pIntoPC))
        ElseIf pFromToDist < 0.01 Then
            ' Extend first
            pOutPath.AddPointCollection(fJoinPC(pRemPC, pIntoPC))
        ElseIf pToToDist < 0.01 Then
            ' flip second then join
            pOutPath.AddPointCollection(fJoinPC(pIntoPC, fFlipPC(pRemPC)))
        End If

        pOutPolyLine.AddGeometry(pOutPath)
        Dim pOutShape As IGeometry = pOutPolyLine
        pOutShape.SpatialReference = pFtInto.ShapeCopy.SpatialReference

        ' update one and remove the other
        pFtInto.Shape = pOutShape
        pUpCur.UpdateFeature(pFtInto)
        pFtRem.Delete()
    Next

    pEd.StopOperation("Unsplit")
End Sub