Lulworth - impressive information. I'm gonna sound pedantic here, but each of these are slightly different from the arrangement for Sainsbury's purchase of the Mem. To extend your summaries:
1. TFL themselves pulled out of the deal for the Northwood redevelopment, not Sainsbury's. The proposed development didn't get to planning. No binding contract in place between TFL & Sainsbury's.
2. Sainsbury's had already bought the old Bradford and Bingley building, and chose not to proceed with development on the land that Sainsbury's themselves owned and are now looking ot sell.
3. In South Ruislip, Sainsbury's already owned a store and were planning to redevelop. They chose to stick with their existing store as a large Asda had been approved for development nearby.
4. In Canterbury, like Ruislip, Sainsbury's already had a store and decided not to redevelop, claiming the scheme would not be financially viable. No contractual arrangement - self owned.
5. Wadebridge - Sainsbury's bought the land and even started development, but chose to mothball. Purchase to original owner completed, but some of the S106 monies are in doubt for associated local development as a result of the mothballing.
6. Tonbridge - Sainsbury's already owned a store on site, but pulled out of redevelopment again claiming the scheme was not financially viable.
In all of the above, it does not appear as though there was a contract in place between Sainsbury's and any other landowner for Sainsbury's to purchase the land and develop as for the Mem.
7. The Hinckley development did proceed and is possibly the most relevant to the Mem. Sainsbury's were pulling out of the deal in May 2013, citing that as the developer Tin Hat was unable to meet its contractual conditions. The council funded the shortfall (bailing out Tin Hat) and Sainsbury's removed their threat and proceeded.
To me, it seems that the removal of the onerous condition surrounding store delivery times (largely funded by Rovers) is similar to the Hinkley bail out in that it helps to satisfy the contractual conditions that make it more difficult for Sainsbury's to pull out of the deal.
Differences - most of the above were under Justin King's reign and not Mike Coupe. Trading conditions have worsened for Sainsbury's.
Additionally, noone apart from the insiders know the actual T&Cs of the contract between Rovers and Sainsbury's.
I remain optimistic.