What on the 15th? Highly unlikely, it’s only 3,000 away fans to Chelsea. Cup semi, I don’t think they will, most of the routes to Wembley are unscathed.
Its probably because the South West route is the only service into Clapham and has you avoiding the tube. The buses from Croydon to Clapham are non advertised to get people onto local bus routes.
I don't think these engineering works will be cancelled they don't directly affect the route to London, just go to London Bridge and change for Jubilee Line.