If Aurigny wanted to axe the ACI-SOU route they wouldn't be buying Dorniers, now would they? They'd simply let the Tris stagger on between ACI and GCI. The simple fact is that politically, it is impossible for Aurigny to drop the ACI-SOU route, no matter what the economics of it. By replacing the Tris with Dorniers they are not only saving themselves money--I serious doubt the DOC of a DO228 is £500ph--but they have opened up the possibility of operating other routes.
The group of enthusiasts in Alderney obviously have their own agenda but they are completely unrealistic. No existing airline in Europe would buy newly-manufactured Tris. To set up a new airline--if that is their ultimate idea--is prohibitively expensive and there are many legislative hoops to jump through. The days of the 'mom and pop' airlines are pretty much done. The infrastructure required by the various authorities simply won't make a small airline economically feasible. Alderney does not exist in some sort of bubble, they would have to comply with all existing regulations and any that come into being in the future. Not the least of the hurdles which would be getting permission for a new airline to fly into SOU. I haven't looked at a SOU SID plate for a while now, but the last time I did Tris got a 'special mention'. Too noisy.
The Tris have had their day. I fully understand nostalgia and the Islanders' affection for them but the Dornier is a vastly more capable aircraft. There has been a load of rubbish talked about how (ultimately) 3 DO228s can't replace 6 Tris, but the simple fact is that all 6 Tris are rarely serviceable at the same time. Due to increased speed, there would be absolutely no problems caused by one DO228 going tech. The morning LCY aircraft will be able to fill-in, even if flights would be delayed. That's assuming that 1 out of three Dorniers will be tech/unavailable at any given time, which in my opinion is a totally unrealistic assumption.