Both do no have to go bankrupt. But if they don't than the non bankrupt partner might end up owing all the debt. For example in the case of a house mortgage in joint names. I believe there is a facility to bankrupt together, but I assume you'd both end up individually bankrupt, just that you go through it together.
In relation to living expense and how this would be worked out have a look at the Insolvency website, they are producing reams of documentation on all of this as they have practically no bankrupties or insolvencies to handle.