Admittedly you did say this is all hypothetical, but it does seem harsh to damn England's selectors for a situation that has never occurred and therefore has no basis for your assumptions. Yes, some would criticise the "looking back" if Butcher & Thorpe were recalled (notably idiot Lawton in "The Independent"), but most serious commentators would not. Certainly not where Thorpe's concerned, anyway, and I can't imagine him not playing in the 1st SA test, whatever happens at The Oval. Butcher, if we're honest, is a slightly different situation. We all know he's done quite well over the last 3 years, but against today's test attacks on today's wickets, an average of 41 over that period isn't *that* special, and, if someone better were to come along, surely that player should replace him. Obviously it's a debateable point whether Key or Bell falls into that category.
As for the Australians, they haven't been completely unwilling to ditch players with a decent track record if they think better options are available. Healey & Slater spring immediately to mind, but I'm sure there are others.