Re: Scottish one
The binding power of independence referendums really depends upon the same thing that underpins all governments: Firepower.
What happens if the result is 'yes?' That looks like it could happen, skimming over the opinion polls. The only way Spain could respond then would be to directly attack political leaders - compile a list of everyone in the Catalan parliament who supported the referendum, arrest them all for sedition. As the police seem to be loyal to Spain rather than Catalonia, there's nothing much anyone in Catalonia could do about it.