Yes they did.
As it happens, I spent a day with the lads and lasses at LATCC some time ago.
The Duty Supervisor told me how the Captain was offered the opportunity to divert to Stansted.
Apparently, the British Airport Authority, owners of Heathrow, were concerned about the loss of an available runway should VS plough up 27L.
The reply from the Captain was unemotional, and very simple.
"Mayday, Mayday, Mayday," and with that, he was vectored unceremoniously to an uneventful landing on 27L.
As for the loss of capacity, I cannot help with the details.
It didn't seem terribly important, so I didn't ask.
Nonetheless, for those that are interested, the BAA provide a service which is matched against safety.
It appears that 42 planes, or movements, an hour is the optimum for safety and service.
That may have changed, given aircraft are often vectored onto final "following a (name the carrier) B747 2.5 miles ahead".