Your problem is very simple here and it will depend on your personal circumstances when you are contacted to complete and if on this date if you are still employed and, based on your current personal circumstances at this time, then you can be asked to complete
The consumer law in Spain is for people who´s personal circumstances have actually changed, they would typically be required to prove unemployment and can prove that they are unable to obtain a mortgage, through normal channels and you have to prove this by getting 3 mortgage refusals, including the builders mortgage
A directive under Spanish Consumer Law can then be excercised but agian it is always advisable to involve your lawyer in this process