I personally cannot wait for the financial demise of Tesco, they are not a considerate neighbour but an all too powerful bully that could not give a care for their continued negative impact on the quality of life for local folks. Dont expect them to care in this instance also.
Don't hold your breath! And for everyone living near a Tesco whose quality of life has been degraded by the store, you'll find ten who welcome the proximity of a large shop that sells almost everything and offers free parking and modern, clean stores with facilities such as toilets. Just ask any independent town centre grocer/clothing store/electrical retailer etc etc. I'm not saying I disagree with your sentiments, but the population vote with their feet and currently most people's feet take them to Tesco!
On the subject of Scillonians heading to Cornwall for pre-planned medical treatment, why can't they go by fixed wing to Land's End or Newquay? The latter is closer to Treliske in any case. And any medical emergencies (which wouldn't have gone by S-61 in any case), there will still be a SAR aircraft at Culdrose.