GROUNDHOG
Yes and no on that one - they could have walked away without founding Air Southwest, but there was nothing to gain then.
In 2000 they took over the remainder of British Airway's lease on PLH, it had something like four or five years left IIRC. At the time they negotiated the 150 year lease with the fantastically juicy 'Armageddon' clause, but it wasn't formally awarded and signed until 2004, around a year after Sutton Harbor founded Air Southwest. In fact the signing was a political football in getting Air Southwest founded.
So yes, when BA (inevitably) pulled out Sutton could have claimed non viability and closed PLH, but back then they wouldn't have benefited from 25% of any proceeds in doing so.