Well... The council can make a Compulsory Purchase Order, which is then followed up by a General Vesting Declaration if the owner still refuses to sell. It's not likely the Council would do it unless there was some pressing reason, such as wanting to redevelop the land for the good of the whole community. (Which may well be the case, but persuading the council of that..?) And the Council couldn't just take possession, they actually have to buy it with hard cash (from our Council Tax!).
There's no such thing as losing your right to land in Scotland, just because you aren't using it. The land has to actually be sold to the peson who is staking the claim. Usually (d'uhh!) the seller is the person who owns the land. But if that person can't be traced (and you have to prove they can't be traced) the buyer can get their solicitor, or a member of their family to sell it to them for a nominal sum (this is an "a non domino" sale). Even then, the sale can be challenged for a period of at least ten years.
If the rightful owner is deceased, the land goes to their heirs. If they have no heirs, it goes to The Queen's and Lord Treasurer's Remembrancer (ie the Government, on behalf of the Queen) who can then pass a good title to the purchasers.
But I'm pretty sure this site is privately owned... so all this debate is academic.
And yes, Porty is a grand place to be!