There's NO Bi-Di working at Feltham.
My apologies for my faux pas and ignorance there, SWT Driver- I should be ashamed of myself since my grandfather was, as I said, a driver! As a mere passenger and partial rail anorak these days, I think I was using the wrong terminology- I meant crossover, didn't I? I trust I'm forgiven in my ignorance.
Anyway, trains have frequently terminated at Feltham and returned over to the 'down' platform (2) during 'routine' engineering works in the past, so obviously it's not something the area is unfamiliar with. Indeed, I'm sure I remember dividing taking place at Feltham rather than Staines in the sixties, but that's another topic entirely.
There is, by the way, a pedestrian track crossing for staff between the SWT office/NR signalling centre, and the down platform, underneath the road bridge (not the affected one) that carries the A244 above the station. Probably very much used at the moment- and you should see how much busier the car park of the SWT office is too, though public car parking in the small car park by the original station entrance on the down side seems to have been suspended to allow for the bustitutions.
As to the local road closures, well I knew that London Road in Twickenham- the A310 road outside the station- often had curtailed bus services on match days, but as far as I know, buses still run through Twickenham town centre, i.e. Heath Road and King Street and then at 'Twickenham [ road ] Junction' by Barclays Bank, buses still turn into Richmond Road heading for East Twickenham, St Margaret's and Richmond.
So there should be nothing stopping a bus service at least as far as Central Twickenham- if there was a safe turning point. Could not Marble Hill Park or York House have been used? The main road closures affect the area around Whitton and Isleworth, so I could understand difficulties there, but I still think bus travel, whether by SWT replacements or TfL buses should be possible to Twickers on Saturday.