So, no. Contracts do not have to be -- and indeed, frequently -- https://en.wikipedia.org/wiki/Sovereign_default#List_of_sove... are not adhered to.
You wish poverty on millions? You wish social unrest? You wish the perpetuation of an unjust financial state of affairs then.
I've said this until I'm blue in the face, the €zone as it exists cannot function without fiscal transfers. That requires _political_ redress. Until that happens sovereign states within the €zone are not playing on a level playing field. Each state gave up a lever of power (sovereign currency) to join the club and a similar virtual lever must be established in return (fiscal transfers). Within the USA there are fiscal transfers. Between regions in sovereign states (Germany, UK, Spain, etc.) there are. The €zone has got to have them.
But nooo - "Pacta sunt servanda". That simple is it? Give me a break.