system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How would Greek exit from eurozone lead to euro collapse, what exactly would happen after Greek exit, step-by-step?

EDIT: It has been pointed out below that there are several "unknowns"  which make the question unanswerable. Perhaps the more generals questions of "How does a banking system collapse?" and "How does a currency collapse, what is the step-by-step process?" are more answerable.

I can only assume these are complex processes with many variables and numerous ways of evolving but a step-by-step analysis of any scenario would be a very interesting read. ELI5.
gpt
Greece exits the Eurozone, unilateral declares that existing debt will be paid back in drachma at some rate (a semi-default). They begin to devalue their currency. They have some rough years because people are wary of taking their worthless pieces of paper in exchange for actual goods and services. Eventually however, Greek labor becomes so cheap that they bounce back to a new normal, poorer than before, but sustainable.

Step two of the Euro crisis is Spain and Italy looking sideways at Greece saying, "hmm, that looks pretty good and we wouldn't even have as bad of a landing since we both have legit economies and actual exports"